A platinum alloy composition

ABSTRACT

A platinum alloy composition consisting, in weight percent, of: 0.0 to 10.0 gold, 0.0 to 5.0 cobalt, 0.0 to 10.0 copper, 0.0 to 7.0 iron, 0.0 to 4.0 gallium, 0.0 to 3.0 indium, 0.0 to 5.0 iridium, 0.0 to 10.0 manganese, 0.0 to 7.0 nickel, 0.0 to 15.0 palladium, 0.0 to 5.0 rhenium, 0.0 to 5.0 rhodium, 0.0 to 10.0 ruthenium, 0.0 to 3.0 tin, 85.0 or more platinum and incidental impurities, wherein two or more of gallium, indium and tin are present in an amount of 0.1 or more, wherein the following equation is satisfied in which W co , W Cu , W Fe , W Ga , W In , W Ni , W Pd , W Sn , W Rh , W Ir , W Au , W Ru , W Re , and W Mn  are the weight percent of cobalt, copper, iron, gallium, indium, nickel, palladium, tin, rhodium, iridium, gold, ruthenium, rhenium, and manganese in the alloy respectively 60+W Pd *2.5+W Rh *3.4+W Ir *6.455+W Au *11.93+W Ru *13.241+W Cu *14.328+W Re *16.6+W Ni *16.9+W Mn *18.48+W Co *18.69+W Fe *21.879+W In *29+W Sn *28.207+W Ga *42.379≥150 and wherein one of the following conditions is satisfied in which W Co , W Cu , W Fe , W Ga , W In , W Ni , W Pd , W Sn , W Mn , W Ru , W Ir , W Rh , W Au , W Pt  and W Re  are the weight percent of cobalt, copper, iron, gallium, indium, nickel, palladium, tin, manganese, ruthenium, iridium, rhodium, gold, platinum and rhenium in the alloy respectively −0.1028*W Co −0.1201*W Cu −0.2113*W Fe −0.3368*W Ga −0.1125*W In −0.1639*W Ni −0.015*W Pd −0.1959*W Sn +17.276261−0.20*W Mn +0.0678*W Ru +0.035*W Ir +0.045*W Rh −0.059*W Au +0.066*W Re ≤16.0 when W Pt &lt;95.0 and −0.1028*W Co −0.1201*W Cu −0.2113*W Fe −0.3368*W Ga −0.1125*W In −0.1639*W Ni −0.015*W Pd −0.1959*W Sn +17.276261−0.20*W Mn +0.0678*W Ru +0.035*W Ir +0.045*W Rh −0.059*W Au +0.066*W Re ≤16.6 when W Pt ≥95.0 and wherein the following equations are satisfied in which W Co , W Cu , W Fe , W Ga , W In , W Ni , W Pd , W Sn , and W Au  are the weight percent of cobalt, copper, iron, gallium, indium, nickel, palladium, tin, and gold in the alloy 0.35 W Au +0.6 W Sn +0.6 W In +W Ga ≤3.75 W Co +W Pd +W Fe +W Ni +W Cu ≥1.0 W Sn +W In +W Ga ≥0.25.

The present invention relates to a platinum alloy composition, inparticular a platinum alloy composition for use in jewellery and analloy composition for jewellery with improved castability and tojewellery.

For jewellery applications pure platinum does not have sufficienthardness to provide wear resistance. To improve the wear resistance ofplatinum alloys, additional elements are added. These elements increasealloy hardness providing increased resistance to wear.

While it is desirable to add elements to platinum to increase hardness,the addition of alloying elements can adversely affect the castabilityof the material. For example, additions of certain elements to Pt willincrease the overall melting temperature of the alloy. A higher meltingtemperature will increase the reaction of molten metal with the mouldmaterial during the casting process and reduce surface quality. A highermelting temperature may also result in reduced alloy fluidity duringcasting as it may be difficult to achieve sufficient ‘superheat’ priorto casting given the already high melting point of pure platinum.

It is an aim of the present invention to provide a platinum alloy withsuitable hardness for jewellery which has reduced melting temperature,and superior casting properties.

The present invention provides a platinum alloy composition consisting,in weight percent, of: 0.0 to 10.0 gold, 0.0 to 5.0 cobalt, 0.0 to 10.0copper, 0.0 to 7.0 iron, 0.0 to 4.0 gallium, 0.0 to 3.0 indium, 0.0 to5.0 iridium, 0.0 to 10.0 manganese, 0.0 to 7.0 nickel, 0.0 to 15.0palladium, 0.0 to 5.0 rhenium, 0.0 to 5.0 rhodium, 0.0 to 10.0ruthenium, 0.0 to 3.0 tin, 85.0 or more platinum and incidentalimpurities, wherein two or more of gallium, indium and tin are presentin an amount of 0.1 or more, wherein the following equation is satisfiedin which W_(Co), W_(Cu), W_(Fe), W_(Ga), W_(In), W_(Ni), W_(Pd), W_(Sn),W_(Rh), W_(Ir), W_(Au), W_(Ru), W_(Re), and W_(Mn) are the weightpercent of cobalt, copper, iron, gallium, indium, nickel, palladium,tin, rhodium, iridium, gold, ruthenium, rhenium, and manganese in thealloy respectively

60+W _(Pd)*2.5+W _(Rh)*3.4+W _(Ir)*6.455+W _(Au)*11.93+W _(Ru)*13.241+W_(Cu)*14.328+W _(Re)*16.6+W _(Ni)*16.9+W _(Mn)*18.48+W _(Co)*18.69+W_(Fe)*21.879+W _(In)*29+W _(Sn)*28.207+W _(Ga)*42.379≥150

-   -   and wherein one of the following conditions is satisfied in        which W_(Co), W_(Cu), W_(Fe), W_(Ga), W_(In), W_(Ni), W_(Pd),        W_(Sn), W_(Mn), W_(Ru), W_(Ir), W_(Rh), W_(Au), W_(Pt) and        W_(Re) are the weight percent of cobalt, copper, iron, gallium,        indium, nickel, palladium, tin, manganese, ruthenium, iridium,        rhodium, gold, platinum and rhenium in the alloy respectively

−0.1028*W _(Co)−0.1201*W _(Cu)−0.2113*W _(Fe)−0.3368*W _(Ga)−0.1125*W_(In)−0.1639*W _(Ni)−0.015*W _(Pd)−0.1959*W _(Sn)+17.276261−0.20*W_(Mn)+0.0678*W _(Ru)+0.035*W _(Ir)+0.045*W _(Rh)−0.059*W _(Au)+0.066*W_(Re)≤16.0 when W _(Pt)<95.0

-   -    and

−0.1028*W _(Co)−0.1201*W _(Cu)−0.2113*W _(Fe)−0.3368*W _(Ga)−0.1125*W_(In)−0.1639*W _(Ni)−0.015*W _(Pd)−0.1959*W _(Sn)+17.276261−0.20*W_(Mn)+0.0678*W _(Ru)+0.035*W _(Ir)+0.045*W _(Rh)−0.059*W _(Au)+0.066*W_(Re)≤16.6 when W _(Pt)≥95.0

-   -    and wherein the following equations are satisfied in which        W_(Co), W_(Cu), W_(Fe), W_(Ga), W_(In), W_(Ni), W_(Pd), W_(Sn),        and W_(Au) are the weight percent of cobalt, copper, iron,        gallium, indium, nickel, palladium, tin, and gold in the alloy

0.35W _(Au)+0.6W _(Sn)+0.6W _(In) +W _(Ga)≤3.75

W _(Co) +W _(Pd) +W _(Fe) +W _(Ni) +W _(Cu)≥1.0

W _(Sn) +W _(In) +W _(Ga)≥0.25.

Such an alloy is suitable for use in jewellery, has a melting pointsignificantly below that of elemental platinum and lower than that ofprior art alloys and has increased hardness compared to elementalplatinum and several commonly used platinum alloys. The alloys accordingto the present invention are well suited for the fabrication ofjewellery and other ornamental articles because they exhibit superiorcastability and mechanical properties relative to a large number ofbenchmarks. In particular, the alloys have a low solidification rangeand lower prevalence of intermetallics making them suitable for castingand subsequent forming without the need for heat treatment.

In an embodiment the platinum alloy composition consists, in weightpercent, of 90.0 or more platinum or sum of platinum and iridium,preferably 95.0 or more platinum or sum of platinum and iridium. Such analloy meets the 900Pt or 950Pt standard for platinum jewelleryrespectively.

In an embodiment the platinum alloy composition satisfies the followingequation in which W_(Co), W_(Cu), W_(Fe), W_(Ga), W_(In), W_(Ni),W_(Pd), W_(Sn), W_(Rh), W_(Ir), W_(Au), W_(Ru), W_(Re), and W_(Mn) arethe weight percent of cobalt, copper, iron, gallium, indium, nickel,palladium, tin, rhodium, iridium, gold, ruthenium, rhenium, andmanganese in the alloy respectively

60+W _(Pd)*2.5+W _(Rh)*3.4+W _(Ir)*6.455+W _(Au)*11.93+W _(Ru)*13.241+W_(Cu)*14.328+W _(Re)*16.6+W _(Ni)*16.9+W _(Mn)*18.48+W _(Co)*18.69+W_(Fe)*21.879+W _(In)*29+W _(Sn)*28.207+W _(Ga)*42.379≥200

-   -   preferably wherein

60+W _(Pd)*2.5+W _(Rh)*3.4+W _(Ir)*6.455+W _(Au)*11.93+W _(Ru)*13.241+W_(Cu)*14.328+W _(Re)*16.6+W _(Ni)*16.9+W _(Mn)*18.48+W _(Co)*18.69+W_(Fe)*21.879+W _(In)*29+W _(Sn)*28.207+W _(Ga)*42.379≥225

-   -   more preferably wherein

60+W _(Pd)*2.5+W _(Rh)*3.4+W _(Ir)*6.455+W _(Au)*11.93+W _(Ru)*13.241+W_(Cu)*14.328+W _(Re)*16.6+W _(Ni)*16.9+W _(Mn)*18.48+W _(Co)*18.69+W_(Fe)*21.879+W _(In)*29+W _(Sn)*28.207+W _(Ga)*42.379≥250

-   -   yet more preferably wherein

60+W _(Pd)*2.5+W _(Rh)*3.4+W _(Ir)*6.455+W _(Au)*11.93+W _(Ru)*13.241+W_(Cu)*14.328+W _(Re)*16.6+W _(Ni)*16.9+W _(Mn)*18.48+W _(Co)*18.69+W_(Fe)*21.879+W _(In)*29+W _(Sn)*28.207+W _(Ga)*42.379≥275

-   -   most preferably wherein

60+W _(Pd)*2.5+W _(Rh)*3.4+W _(Ir)*6.455+W _(Au)*11.93+W _(Ru)*13.241+W_(Cu)*14.328+W _(Re)*16.6+W _(Ni)*16.9+W _(Mn)*18.48+W _(Co)*18.69+W_(Fe)*21.879+W _(In)*29+W _(Sn)*28.207+W _(Ga)*42.379≥300

Such an alloy has superior hardness making it suitable for jewellery.

In an embodiment the platinum alloy composition satisfies the followingequation in which W_(Co), W_(Cu), W_(Fe), W_(Ga), W_(In), W_(Ni),W_(Pd), W_(Sn), W_(Rh), W_(Ir), W_(Au), W_(Ru), W_(Re), and W_(Mn) arethe weight percent of cobalt, copper, iron, gallium, indium, nickel,palladium, tin, rhodium, iridium, gold, ruthenium, rhenium, andmanganese in the alloy respectively

60+W _(Pd)*2.5+W _(Rh)*3.4+W _(Ir)*6.455+W _(Au)*11.93+W _(Ru)*13.241+W_(Cu)*14.328+W _(Re)*16.6+W _(Ni)*16.9+W _(Mn)*18.48+W _(Co)*18.69+W_(Fe)*21.879+W _(In)*29+W _(Sn)*28.207+W _(Ga)*42.379≤280

-   -   preferably wherein

60+W _(Pd)*2.5+W _(Rh)*3.4+W _(Ir)*6.455+W _(Au)*11.93+W _(Ru)*13.241+W_(Cu)*14.328+W _(Re)*16.6+W _(Ni)*16.9+W _(Mn)*18.48+W _(Co)*18.69+W_(Fe)*21.879+W _(In)*29+W _(Sn)*28.207+W _(Ga)*42.379≤260

-   -   more preferably wherein

60+W _(Pd)*2.5+W _(Rh)*3.4+W _(Ir)*6.455+W _(Au)*11.93+W _(Ru)*13.241+W_(Cu)*14.328+W _(Re)*16.6+W _(Ni)*16.9+W _(Mn)*18.48+W _(Co)*18.69+W_(Fe)*21.879+W _(In)*29+W _(Sn)*28.207+W _(Ga)*42.379≤240.

Such an alloy may be more suitable for jewellery applications where gemsetting is necessary.

In an embodiment the platinum alloy composition satisfies the followingequation in which W_(Co), W_(Cu), W_(Fe), W_(Ga), W_(In), W_(Ni),W_(Pd), W_(Sn), W_(Rh), W_(Ir), W_(Au), W_(Ru), W_(Re), and W_(Mn) arethe weight percent of cobalt, copper, iron, gallium, indium, nickel,palladium, tin, rhodium, iridium, gold, ruthenium, rhenium, andmanganese in the alloy respectively

−0.1*W _(Co)−0.4933*W _(Cu)−0.32*W _(Fe)−1.16377*W _(Ga)−0.54278*W_(In)−0.08612*W _(Ni)+0.06915*W _(Pd)−0.69928*W _(Sn)+4.169+0.04*W_(Mn)+0.133*W _(Au)≤3.941

-   -   preferably wherein

−0.1*W _(Co)−0.4933*W _(Cu)−0.32*W _(Fe)−1.16377*W _(Ga)−0.54278*W_(In)−0.08612*W _(Ni)+0.06915*W _(Pd)−0.69928*W _(Sn)+4.169+0.04*W_(Mn)+0.133*W _(Au)≤3.5

-   -   more preferably wherein

−0.1*W _(Co)−0.4933*W _(Cu)−0.32*W _(Fe)−1.16377*W _(Ga)−0.54278*W_(In)−0.08612*W _(Ni)+0.06915*W _(Pd)−0.69928*W _(Sn)+4.169+0.04*W_(Mn)+0.133*W _(Au)≤3.0

-   -   even more preferably wherein

−0.1*W _(Co)−0.4933*W _(Cu)−0.32*W _(Fe)−1.16377*W _(Ga)−0.54278*W_(In)−0.08612*W _(Ni)+0.06915*W _(Pd)−0.69928*W _(Sn)+4.169+0.04*W_(Mn)+0.133*W _(Au)≤2.5

Such an alloy has superior resistance to hot cracking.

In an embodiment the platinum alloy composition satisfies the followingequation in which W_(Co), W_(Cu), W_(Fe), W_(Ga), W_(In), W_(Ni),W_(Pd), W_(Sn), W_(Mn), W_(Ru), W_(Ir), W_(Rh), W_(Au) and W_(Re) arethe weight percent of cobalt, copper, iron, gallium, indium, nickel,palladium, tin, manganese, ruthenium, iridium, rhodium, gold and rheniumin the alloy respectively

−0.1028*W _(Co)−0.1201*W _(Cu)−0.2113*W _(Fe)−0.3368*W _(Ga)−0.1125*W_(In)−0.1639*W _(Ni)−0.015*W _(Pd)−0.1959*W _(Sn)+17.276261−0.20*W_(Mn)+0.0678*W _(Ru)+0.035*W _(Ir)+0.045*W _(Rh)+0.059*W _(Au)+0.066*W_(Re)≤16.0

-   -   preferably wherein

−0.1028*W _(Co)−0.1201*W _(Cu)−0.2113*W _(Fe)−0.3368*W _(Ga)−0.1125*W_(In)−0.1639*W _(Ni)−0.015*W _(Pd)−0.1959*W _(Sn)+17.276261−0.20*W_(Mn)+0.0678*W _(Ru)+0.035*W _(Ir)+0.045*W _(Rh)+0.059*W _(Au)+0.066*W_(Re)≤15.5

-   -   more preferably wherein

−0.1028*W _(Co)−0.1201*W _(Cu)−0.2113*W _(Fe)−0.3368*W _(Ga)−0.1125*W_(In)−0.1639*W _(Ni)−0.015*W _(Pd)−0.1959*W _(Sn)+17.276261−0.20*W_(Mn)+0.0678*W _(Ru)+0.035*W _(Ir)+0.045*W _(Rh)+0.059*W _(Au)+0.066*W_(Re)≤15.0

-   -   even more preferably wherein

−0.1028*W _(Co)−0.1201*W _(Cu)−0.2113*W _(Fe)−0.3368*W _(Ga)−0.1125*W_(In)−0.1639*W _(Ni)−0.015*W _(Pd)−0.1959*W _(Sn)+17.276261−0.20*W_(Mn)+0.0678*W _(Ru)+0.035*W _(Ir)+0.045*W _(Rh)+0.059*W _(Au)+0.066*W_(Re)≤14.5

Such an alloy has a lower melting temperature and therefore reacts lesswith mould walls during casting and so has superior surface quality.

In an embodiment the platinum alloy composition consists, in weightpercent, of 5.0 or less nickel. Such an alloy will be unlikely to causea reaction on human skin contact.

In an embodiment the platinum alloy composition consists, in weightpercent, of 3.0 or less iridium. Such an alloy has reduced cost.

In an embodiment the platinum alloy composition consists, in weightpercent, of 3.0 or less rhodium. Such an alloy has reduced cost.

In an embodiment the platinum alloy composition consists, in weightpercent, of 5.0 or less ruthenium, preferably 3.0 or less ruthenium.Such an alloy will have superior casting properties.

In an embodiment the platinum alloy composition consists, in weightpercent, of 3.0 or less rhenium. Such an alloy will have a lower meltingtemperature leading to superior casting properties.

In an embodiment the platinum alloy satisfies the following equation inwhich W_(Ga), W_(In), and W_(Sn) are the weight percent of gallium,indium, and tin in the alloy W_(Sn)+W_(In)+W_(Ga)≥0.40. Such an alloywill have a higher hardness

In an embodiment the platinum alloy composition consists, in weightpercent, of 2.5 or less indium, preferably 2.0 or less indium. Such analloy will produce fewer intermetallic phases on cooling and has a lowersolidification range.

In an embodiment the platinum alloy composition of any of the precedingclaims, consisting, in weight percent, of 2.5 or less tin, preferably2.0 or less tin. Such an alloy will produce fewer intermetallic phaseson cooling and has a lower solidification range.

In an embodiment at 1000° C. the alloy composition comprises 0.55 ormore volume fraction solid solution FCC gamma phase, preferably 0.6 ormore volume fraction gamma phase, more preferably 0.7 or more volumefraction gamma phase, even more preferably 0.8 or more volume fractiongamma phase, most preferably 0.9 or more volume fraction gamma phase.Such an alloy is desirable as the risk of reduced ductility is lowered.

In an embodiment the alloy composition has a solidification range of200° C. or less, preferably wherein the alloy composition has asolidification range of 150° C. or less, more preferably wherein thealloy composition has a solidification range of 125° C. or less, morepreferably wherein the alloy composition has a solidification range of100° C. or less, even more preferably wherein the alloy composition hasa solidification range of 75° C. or less, most preferably wherein thealloy composition has a solidification range of 50° C. or less. Such analloy will have superior casting properties with lower propensity forpore formation.

In an embodiment the platinum alloy composition of any preceding claim,wherein at least two, preferably at least three, elements selected fromthe following list are present: gold, cobalt, copper, iron, gallium,indium, iridium, manganese, nickel, palladium, rhenium, rhodium,ruthenium, tin. Such alloys have been shown to exhibit the bestcombination of properties sought in this application.

In an embodiment indium and tin are present in an amount of 0.1 or morein the platinum alloy composition. Such an alloy has reducedintermetallic precipitation.

In an embodiment the platinum alloy composition of any of the precedingclaims, wherein the following equation is satisfied in which W_(Ga),W_(Sn), and W_(Au) are the weight percent of gallium, tin and gold inthe alloy respectively

W_(Au)*0.35+W _(Sn)*0.6+W _(In)*0.6+W _(Ga)≤3.0

Such an alloy is likely to have a lower solidification range.

In an embodiment the platinum alloy composition satisfies the followingequation in which W_(Co), W_(Fe), W_(Ni), and W_(Pd) are the weightpercent of cobalt, iron, nickel, and palladium in the alloy respectively

(W _(Co) +W _(Pd))/11+(W _(Fe) +W _(Ni))/2.2≥1.0

Such an alloy is likely to be easily castable without the addition ofother alloying elements as it likely to have a low melting point whileretaining a narrow solidification range.

In an embodiment the platinum alloy composition of any of the precedingclaims, consisting, in weight percent, of 5.0 or less gold, preferably3.0 or less gold. Such an alloy has reduced solidification range.

In an embodiment the platinum alloy composition of any of the precedingclaims, consisting, in weight percent, of 9.0 or less copper, preferably8.0 or less copper. Such an alloy has improved castability as formationof slag during melting for casting is less likely and the alloy has alower solidification range.

In an embodiment the platinum alloy composition consists, in weightpercent, of 2.0 or less gallium, preferably 1.5 or less gallium. Such analloy has a lower solidification range and lower chance of precipitationof intermetallic phases.

In an embodiment the platinum alloy composition the following equationis satisfied in which W_(Ir) and W_(Ru) are the weight percent ofiridium and ruthenium in the alloy respectively

2.5W _(Ir)+3.0W _(Ru)≤7.5

Such an alloy has reduced melting temperature.

In an embodiment the platinum alloy composition of any of theproceedings claims, wherein on cooling from liquid, gamma phase is firstto form in which all alloying elements are in solid solution. Such analloy will have superior ductility as the formation of large brittlegrains made of intermetallic phases on solidification will be avoided.

In an embodiment the platinum alloy composition consists, in weightpercent, 0.0 to 1.0 total sum weight percent of gold, iridium,manganese, rhenium, rhodium, and ruthenium. Such an alloy is preferredbecause it is possible to achieve favourable properties in terms ofharness and castability (e.g. low melting point, low solidificationrange and/or low hot cracking propensity) whilst maintaining a highplatinum content.

In an embodiment the platinum alloy composition satisfies the followingequation in which W_(Co), W_(Cu), W_(Fe), W_(Ga), W_(In), W_(Ni),W_(Pd), W_(Sn), W_(Mn), W_(Ru), W_(Ir), W_(Rh), W_(Au) and W_(Re) arethe weight percent of cobalt, copper, iron, gallium, indium, nickel,palladium, tin, manganese, ruthenium, iridium, rhodium, gold and rheniumin the alloy respectively

0.041W _(Au) W _(Co)+0.122W _(Au) W _(In)+1.96W _(Au) W _(Ni)+1.87W_(Au) W _(Sn)+0.903W _(Au) ²+1.74W _(Co) W _(Ga)+13.4W _(Co) W_(In)+1.24W _(Co) W _(Mn)+5.04W _(Co) W _(Sn)+1.02W _(Co) ²+8.97W _(Cu)W _(Fe)+1.74W _(Cu) W _(Ga)+4.38W _(Cu) W _(In)+1.16W _(Cu) W_(Mn)+0.491W _(Cu) W _(Ni)+3.69W _(Cu) W _(Sn)+0.22W _(Cu) ²+1.68W _(Fe)W _(Ga)+3.31W _(Fe) W _(In)−1.26W _(Fe) W _(Mn)+5.07W _(Fe) W_(Sn)+0.199W _(Fe) ²+5.35W _(Ga) W _(In)+0.086W _(Ga) W _(Mn)+3.27W_(Ga) W _(Re)+33.3W _(Ga) W _(Rh)+4.56W _(Ga) W _(Ru)+2.21W _(Ga) W_(Sn)+29.0W _(Ga)+8.49W _(Ga) ²+9.09W _(In) W _(Mn)−0.28W _(In) W_(Ni)+15.4W _(In) W _(Rh)+0.992W _(In) W _(Ru)+11.7W _(In)+6.68W _(In)²+0.863W _(Ir) ²+5.73W _(Mn) W _(Ni)−0.02W _(Mn) W _(Ru)+5.68W _(Mn) W_(Sn)+18.4W _(Mn)−0.89W _(Mn) ²+0.49W _(Ni) W _(Ru)+0.186W _(Ni) ²+4.48W_(Re) W _(Sn)+1.15W _(Re) ²−5.11W _(Rh) W _(Sn)+2.04W _(Rh) ²+0.885W_(Ru) W _(Sn)+1.28W _(Ru) ²+1.58W _(Sn)+9.49W _(Sn) ²11.6≥140

preferably

0.041W _(Au) W _(Co)+0.122W _(Au) W _(In)+1.96W _(Au) W _(Ni)+1.87W_(Au) W _(Sn)+0.903W _(Au) ²+1.74W _(Co) W _(Ga)+13.4W _(Co) W_(In)+1.24W _(Co) W _(Mn)+5.04W _(Co) W _(Sn)+1.02W _(Co) ²+8.97W _(Cu)W _(Fe)+1.74W _(Cu) W _(Ga)+4.38W _(Cu) W _(In)+1.16W _(Cu) W_(Mn)+0.491W _(Cu) W _(Ni)+3.69W _(Cu) W _(Sn)+0.22W _(Cu) ²+1.68W _(Fe)W _(Ga)+3.31W _(Fe) W _(In)−1.26W _(Fe) W _(Mn)+5.07W _(Fe) W_(Sn)+0.199W _(Fe) ²+5.35W _(Ga) W _(In)+0.086W _(Ga) W _(Mn)+3.27W_(Ga) W _(Re)+33.3W _(Ga) W _(Rh)+4.56W _(Ga) W _(Ru)+2.21W _(Ga) W_(Sn)+29.0W _(Ga)+8.49W _(Ga) ²+9.09W _(In) W _(Mn)−0.28W _(In) W_(Ni)+15.4W _(In) W _(Rh)+0.992W _(In) W _(Ru)+11.7W _(In)+6.68W _(In)²+0.863W _(Ir) ²+5.73W _(Mn) W _(Ni)−0.02W _(Mn) W _(Ru)+5.68W _(Mn) W_(Sn)+18.4W _(Mn)−0.89W _(Mn) ²+0.49W _(Ni) W _(Ru)+0.186W _(Ni) ²+4.48W_(Re) W _(Sn)+1.15W _(Re) ²−5.11W _(Rh) W _(Sn)+2.04W _(Rh) ²+0.885W_(Ru) Sn+1.28W _(Ru) ²+1.58W _(Sn)+9.49W _(Sn) ²11.6≥120

more preferably

0.041W _(Au) W _(Co)+0.122W _(Au) W _(In)+1.96W _(Au) W _(Ni)+1.87W_(Au) W _(Sn)+0.903W _(Au) ²+1.74W _(Co) W _(Ga)+13.4W _(Co) W_(In)+1.24W _(Co) W _(Mn)+5.04W _(Co) W _(Sn)+1.02W _(Co) ²+8.97W _(Cu)W _(Fe)+1.74W _(Cu) W _(Ga)+4.38W _(Cu) W _(In)+1.16W _(Cu) W_(Mn)+0.491W _(Cu) W _(Ni)+3.69W _(Cu) W _(Sn)+0.22W _(Cu) ²+1.68W _(Fe)W _(Ga)+3.31W _(Fe) W _(In)−1.26W _(Fe) W _(Mn)+5.07W _(Fe) W_(Sn)+0.199W _(Fe) ²+5.35W _(Ga) W _(In)+0.086W _(Ga) W _(Mn)+3.27W_(Ga) W _(Re)+33.3W _(Ga) W _(Rh)+4.56W _(Ga) W _(Ru)+2.21W _(Ga) W_(Sn)+29.0W _(Ga)+8.49W _(Ga) ²+9.09W _(In) W _(Mn)−0.28W _(In) W_(Ni)+15.4W _(In) W _(Rh)+0.992W _(In) W _(Ru)+11.7W _(In)+6.68W _(In)²+0.863W _(Ir) ²+5.73W _(Mn) W _(Ni)−0.02W _(Mn) W _(Ru)+5.68W _(Mn) W_(Sn)+18.4W _(Mn)−0.89W _(Mn) ²+0.49W _(Ni) W _(Ru)+0.186W _(Ni) ²+4.48W_(Re) W _(Sn)+1.15W _(Re) ²−5.11W _(Rh) W _(Sn)+2.04W _(Rh) ²+0.885W_(Ru) W _(Sn)+1.28W _(Ru) ²+1.58W _(Sn)+9.49W _(Sn) ²11.6≥100

even more preferably

0.041W _(Au) W _(Co)+0.122W _(Au) W _(In)+1.96W _(Au) W _(Ni)+1.87W_(Au) W _(Sn)+0.903W _(Au) ²+1.74W _(Co) W _(Ga)+13.4W _(Co) W_(In)+1.24W _(Co) W _(Mn)+5.04W _(Co) W _(Sn)+1.02W _(Co) ²+8.97W _(Cu)W _(Fe)+1.74W _(Cu) W _(Ga)+4.38W _(Cu) W _(In)+1.16W _(Cu) W_(Mn)+0.491W _(Cu) W _(Ni)+3.69W _(Cu) W _(Sn)+0.22W _(Cu) ²+1.68W _(Fe)W _(Ga)+3.31W _(Fe) W _(In)−1.26W _(Fe) W _(Mn)+5.07W _(Fe) W_(Sn)+0.199W _(Fe) ²+5.35W _(Ga) W _(In)+0.086W _(Ga) W _(Mn)+3.27W_(Ga) W _(Re)+33.3W _(Ga) W _(Rh)+4.56W _(Ga) W _(Ru)+2.21W _(Ga) W_(Sn)+29.0W _(Ga)+8.49W _(Ga) ²+9.09W _(In) W _(Mn)−0.28W _(In) W_(Ni)+15.4W _(In) W _(Rh)+0.992W _(In) W _(Ru)+11.7W _(In)+6.68W _(In)²+0.863W _(Ir) ²+5.73W _(Mn) W _(Ni)−0.02W _(Mn) W _(Ru)+5.68W _(Mn) W_(Sn)+18.4W _(Mn)−0.89W _(Mn) ²+0.49W _(Ni) W _(Ru)+0.186W _(Ni) ²+4.48W_(Re) W _(Sn)+1.15W _(Re) ²−5.11W _(Rh) W _(Sn)+2.04W _(Rh) ²+0.885W_(Ru) W _(Sn)+1.28W _(Ru) ²+1.58W _(Sn)+9.49W _(Sn) ²11.6≥80

most preferably

0.041W _(Au) W _(Co)+0.122W _(Au) W _(In)+1.96W _(Au) W _(Ni)+1.87W_(Au) W _(Sn)+0.903W _(Au) ²+1.74W _(Co) W _(Ga)+13.4W _(Co) W_(In)+1.24W _(Co) W _(Mn)+5.04W _(Co) W _(Sn)+1.02W _(Co) ²+8.97W _(Cu)W _(Fe)+1.74W _(Cu) W _(Ga)+4.38W _(Cu) W _(In)+1.16W _(Cu) W_(Mn)+0.491W _(Cu) W _(Ni)+3.69W _(Cu) W _(Sn)+0.22W _(Cu) ²+1.68W _(Fe)W _(Ga)+3.31W _(Fe) W _(In)−1.26W _(Fe) W _(Mn)+5.07W _(Fe) W_(Sn)+0.199W _(Fe) ²+5.35W _(Ga) W _(In)+0.086W _(Ga) W _(Mn)+3.27W_(Ga) W _(Re)+33.3W _(Ga) W _(Rh)+4.56W _(Ga) W _(Ru)+2.21W _(Ga) W_(Sn)+29.0W _(Ga)+8.49W _(Ga) ²+9.09W _(In) W _(Mn)−0.28W _(In) W_(Ni)+15.4W _(In) W _(Rh)+0.992W _(In) W _(Ru)+11.7W _(In)+6.68W _(In)²+0.863W _(Ir) ²+5.73W _(Mn) W _(Ni)−0.02W _(Mn) W _(Ru)+5.68W _(Mn) W_(Sn)+18.4W _(Mn)−0.89W _(Mn) ²+0.49W _(Ni) W _(Ru)+0.186W _(Ni) ²+4.48W_(Re) W _(Sn)+1.15W _(Re) ²−5.11W _(Rh) W _(Sn)+2.04W _(Rh) ²+0.885W_(Ru) W _(Sn)+1.28W _(Ru) ²+1.58W _(Sn)+9.49W _(Sn) ²11.6≥60

Such an alloy has lowered solidification range leading to bettercastability, particularly less porosity on casting.

In an embodiment the platinum alloy composition satisfies the followingequation in which W_(Co), W_(Cu), W_(Fe), W_(Ni), and W_(Pd) are theweight percent of cobalt, copper, iron, nickel and palladium in thealloy W_(Co)+W_(Pd)+W_(Fe)+W_(Ni)+W_(Cu)≥2.0. Such an alloy has a lowermelting point without dramatic increase in solidification range.

In an embodiment the two or more of gallium, indium and tin are presentin an amount of 0.25 or more, preferably wherein the two or more ofgallium, indium and tin are present in an amount of 0.5 or more. Such analloy has increased hardness.

In an embodiment the platinum alloy composition satisfies the followingequation in which W_(Co), W_(Fe), and W_(Ni), are the weight percent ofcobalt, iron, and nickel in the alloy 3.0≤W_(Co)+W_(Fe)+W_(Ni)≤4.5. Suchan alloy, particularly in the absence of copper and palladium hasreduced melting point without a corresponding increase in solidificationrange.

In an embodiment the platinum alloy composition satisfies the followingequation in which W_(Ga), W_(In), and W_(Sn), are the weight percent ofgallium, indium and tin in the alloy 0.4≤W_(Ga)+W_(In)+W_(Sn)≤2.2. Thisgives an alloy with superior hardness without a corresponding increasein solidification range.

In an embodiment the platinum alloy composition is made up of 95 weightpercent or more of platinum and satisfies the following equation inwhich W_(Co), W_(Fe), and W_(Ni), are the weight percent of cobalt,iron, and nickel in the alloy 3.0≤W_(Co)+W_(Fe)W_(Ni)≤4.5 as well as thefollowing equation in which W_(Ga), W_(In), and W_(Sn), are the weightpercent of gallium, indium and tin in the alloy0.4≤W_(Ga)+W_(In)+W_(Sn)≤2.2. Such an alloy has a good balance ofcastability and hardness while still meeting the 950 platinumhallmarking requirements.

In an embodiment of the platinum alloy composition the two or more ofgallium, indium and tin are indium and gallium and the followingequation is satisfied in which W_(Ga) and W_(In), are the weight percentof gallium and indium in the alloy 0.5 W_(In)≤W_(Ga)≤1.5 W_(In). Such analloy has reduced chance of intermetallic precipitation.

In an embodiment of the platinum alloy composition the two or more ofgallium, indium and tin are tin and gallium and the following equationis satisfied in which W_(Ga) and W_(Sn), are the weight percent ofgallium and tin in the alloy 0.5 W_(Sn)≤W_(Ga)≤1.5 W_(Sn). Such an alloyhas reduced chance of intermetallic precipitation.

In an embodiment of the platinum alloy composition the two or more ofgallium, indium and tin are indium and tin and the following equation issatisfied in which W_(In), and W_(Sn), are the weight percent of indiumand tin in the alloy 0.5 W_(In)≤W_(Sn)≤1.5 W_(In). Such an alloy hasreduced chance of intermetallic precipitation.

In an embodiment of the platinum alloy composition the two or more ofgallium, indium and tin are indium, tin and gallium and the followingequations are satisfied in which W_(Ga), W_(In), and W_(Sn), are theweight percent of gallium, indium and tin in the alloy 0.3W_(In)≤W_(Ga)≤1.3 W_(In); 0.3 W_(Sn)≤W_(Ga)≤1.3 W_(Sn); 0.3W_(In)≤W_(Sn)≤1.3 W_(In). Such an alloy has reduced chance ofintermetallic precipitation.

The term “consisting of” is used herein to indicate that 100% of thecomposition is being referred to and the presence of additionalcomponents is excluded so that percentages add up to 100%.

The invention will be more fully described, by way of example only, withreference to the accompanying drawings in which:

FIG. 1 shows predicted hardness values vs the melting point index for arange of compositions. Benchmark jewellery alloys are overlaid forcomparison. The hatched polygon shows the improvement achievable overthe benchmark alloys with the present invention.

FIG. 2 is a comparison of gamma prime volume fraction and melting pointindex for a range of compositions the hatched polygon shows a preferredarea and some benchmark alloys are shown too.

FIG. 3 shows predicted hot cracking index vs the melting point index fora range of compositions. Benchmark jewellery alloys are overlaid forcomparison. The hatched polygon shows a preferred area.

FIG. 4 shows predicted solidification range values vs the melting pointindex for a range of compositions. Benchmark jewellery alloys areoverlaid for comparison. The hatched polygon shows a preferred area.

FIG. 5 shows the amount of hard intermetallic phases (in atomic percent)formed due to segregation during the solidification of platinum alloyscontaining 5.0 wt % of cobalt and 4.9X wt % where X is any combinationof gallium, indium and tin which adds up to 1. The values were obtainedby Scheil-Gulliver thermodynamic calculations which is a widely acceptedway of modelling the fraction of various phases in the as-cast state.The hard intermetallic phases (‘terminal intermetallics’) areundesirable as they reduce the ductility of the alloy and may causemachining and forming issues. The amount of terminal intermetallics islowest when all three elements (gallium, indium and tin) are present.

FIG. 6 shows the shape of test castings.

FIG. 7 shows experimental results of the test castings for three alloycompositions showing hardness, grid fill and porosity.

FIG. 8 compares the machinability of an alloy of the present inventionwith a comparative example.

FIG. 9 compares castability of an alloy of the present invention with acomparative example.

The hardness of platinum alloys is derived from two chemicallydetermined mechanisms:

-   -   I. solid-solution hardening—achieved by solute elements        distorting the lattice of the platinum metal due to difference        in atomic radius.    -   II. Precipitation hardening—for elements added which are outside        the solubility limit of platinum secondary phases may occur.        These phases increase the alloys resistance to deformation.

While it is desirable to add elements to platinum to increase thehardness, the additions of alloying elements can adversely affect thecastability of the material in the following ways:

-   -   I. Increased melting temperature—Additions of certain elements        to Pt will increase the overall melting temperature of the        alloy. A higher melting temperature will increase the reaction        of molten metal with the mould material during casting process        and reduce surface quality. A higher melting temperature may        also result in reduced alloy fluidity during casting as it may        be difficult to achieve sufficient ‘superheat’ prior to casting        given the already high melting point of pure platinum. Although        some alloying elements traditionally used to harden platinum        alloys do reduce the melting point, the present inventors have        found that use of other alloying elements or certain        combinations of alloying elements can reduce the melting        temperature even further.    -   II. Casting micro-porosity—During the later stages of        solidification during casting liquid metal becomes trapped        between dendritic arms formed during solidification. The        shrinkage of this trapped liquid results in pore formation. The        pores that form are often visible after casting and will make a        cast jewellery item unacceptable in terms of visual appearance.        Alloying additions which cause significant volume change in an        alloy during solidification and/or those elements that segregate        excessively are known to increase the tendency for        micro-porosity.    -   III. Hot tearing—Alloys which have a very wide solidification        temperature range suffer from a combination of increasing        thermal stress arising from the reducing temperature combined        with limited mechanical strength due to liquid films between        growing grains. The combination of increasing stress and poor        mechanical strength leads to tearing of the metal at high        temperature resulting in a scrapped component.

Superior castability is achieved in the present invention by optimisingseveral material properties, reflected in merit indices. These includethe melting point index and optionally the hot cracking index. Theirvalues are correlated to the risk of typical casting defects: shrinkageporosity, gas porosity, formation of inclusions, poor surface finish andpoor form filling.

Superior mechanical properties are achieved by improving wear resistanceand gem setting ability by increasing hardness. The alloys in theinvention have a tunable hardness and a hardness of 150 HV or more canbe achieved, offering the potential to trade off the ease of formabilityfor improved wear resistance, depending on the application.

In addition, the as-cast microstructures of the alloys can havesufficient ductility which facilitates further processing steps such asgem setting. The inventors have determined that this can be achieved ifthe composition has at least 0.3 volume fraction of ductile gamma Ptmatrix at 1000° C. A higher level of gamma phase is desirable as thisfurther increases the ductility. The as-cast microstructure may not bethe same as the equilibrium microstructure at 1000° C.

A modelling-based approach used for the isolation of new grades ofplatinum alloys addressing at least some of the above issues isdescribed here. This approach utilises a framework of computationalmaterials models combined with machine learning to estimatedesign-relevant properties across a very broad compositional space. Inprinciple, this alloy design tool allows the so-called inverse problemto be solved; identifying optimum alloy compositions that best satisfy aspecified set of design constraints.

The first step in the design process is the definition of an elementallist along with the associated upper and lower compositional limits. Thecompositional limits for each of the elemental additions considered inthis invention—referred to as the “alloy design space”—are detailed inTable 1. These limits were selected by the inventors on the basis of theexplanations given below. Some of the insights are from metallurgicalexperience whilst others, such as the effects on melting point,castability of the platinum alloys and presence of intermetallic phaseshave been established by the inventors based on thermodynamiccalculations described below on a wider range of compositions than setout in Table 1.

TABLE 1 The composition range searched using the ABD ® method andclaimed by the invention. Bounds/wt % Ni Cr Pd Sn Co Fe Cu Ru Rh Ir AuIn Ga Al Re Mn Ti Pt Lower 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 85 Upper7.0 0 15 3 5 7 10 10 5 5 10 3 5 0 5 10 0

It is relatively easy to increase the hardness of pure platinum byadding alloying elements. However, doing this at the same time asmaintaining good castability is not so easy. Among other things, itrequires limiting any rise in solidification range of the alloy causedby introduction of alloying elements, avoiding harmful precipitation ofintermetallic phases in the final stages of solidification, and avoidingthe formation of slag caused by reactive elements, all of which causecasting defects. Some elements which would otherwise be suitable tomeeting at least some of these conflicting requirements must be limitedfor other reasons. Bearing this in mind, the elements and their rangesin Table 1 were selected for the following reasons:

The minimum amount of platinum in the alloys in weight percent was setto 85.0 as this is a minimum acceptable amount of platinum for jewelleryapplications. In some cultures, any iridium content in a platinum alloyis considered equivalent to platinum meaning that the platinum contentof an alloy is considered as being equivalent the sum of platinum andiridium. Preferably the minimum amount of platinum (or sum of platinumand iridium) in weight percent is 90.0 to adhere to internationallyrecognised standards for platinum jewellery for example 900 Pt (90 wt %platinum). Desirably a minimum amount of platinum (or sum of platinumand iridium) in weight percent is 95.0 to adhere to 950 Pt (95 wt %platinum).

Nickel, cobalt, copper, iron and manganese: all lower the melting pointof pure Pt and increase hardness by a combination of solid solution andprecipitation strengthening. In addition, they are relativelyunreactive, meaning their alloys with Pt can be repeatedly remeltedwithout appreciably changing the composition of the alloy due toreactions with the atmosphere, crucible walls or mould walls. Cobalt,manganese and iron amounts are limited in Table 1 because case additionsbeyond the ranges specified in Table 1 are unlikely to bring additionalbenefits as they may not appreciably reduce the melting point further,may result in an excessive fraction of intermetallic phases upon coolingof the casting or may increase the solidification range. Additionallyhigh cobalt can render an alloy ferromagnetic which can causefabrication issues, iron may cause undesirable ferromagnetism and canalso form an intermetallic phase at high temperatures which is suspectedto harm ductility and high manganese can evaporate from melt therebycausing processing issues. Each of these elements may independently ofone another be limited to 10.0 wt % or less. For nickel, there is aconcern about its use in jewellery applications because of allergyconcerns. Therefore the amount of nickel is kept at 7.0 wt % or less,preferably 5.0 wt % or less or even 4.0 wt % or less. On the other handnickel is particularly useful for the purposes given above for thisgroup of elements and so nickel is preferably present in an amount of3.0 wt % or more. Copper is limited to 10.0 wt % or less because it isrelatively easily oxidised compared to the other elements in this groupmeaning that formation of slag during melting for casting is morelikely. Slag formation is undesirable. Additionally, copper has beenfound to increase solidification range at higher concentrations, whichis undesirable. Therefore, copper is preferably limited to 9.0 wt % orless, more desirably 8.0 wt % or less.

Gold has a small effect of reducing the melting temperature of platinumalloys at low concentrations and increases hardness. But gold increasessolidification range and so is limited to 10.0 wt % or lower. Preferablygold is limited to 5.0 wt % or 3.0 wt % or less due to its adverseeffect on solidification range. Preferably gold is absent in the alloyas its presence can hinder recyclability due to difficulty in separatingit from platinum.

Palladium slightly increases hardness by a combination of solid solutionand precipitation strengthening. Palladium has only a slightly reducingeffect on the melting temperature and so must be supplemented by otheralloying elements to reduce the melting point sufficiently (equation(1)). However, palladium is unreactive and so is limited in Table 1 onlyby the minimum required amount of platinum. Thus, in an embodiment thealloy contains palladium and at least two further alloying elements (twoor more selected from tin, indium and gallium, as described below). Inan embodiment, palladium is absent in the alloy as its presence canhinder recyclability due to difficulty in separating it from platinum(in which case one or more of cobalt, iron, nickel and copper ispresent, as described below). In addition, palladium is currently morethan twice the cost of platinum and is therefore undesirable as itincreases the cost of the alloy. Furthermore, platinum-palladium alloysare known to be poorly workable—the palladium content is thereforepreferably reduced to 5.0wt % or less when good workability is to beachieved. In an embodiment the alloy is essentially palladium free (i.e.consists of 0.0 wt % or less).

Rhodium, iridium, ruthenium and rhenium: These elements are very noblemeaning their alloys with Pt can be repeatedly remelted withoutappreciably changing the composition of the alloy due to reactions withthe atmosphere, crucible walls or mould walls. In addition, theyincrease hardness by solid solution strengthening. However, excessiveadditions of iridium and/or rhodium and/or rhenium may appreciablyincrease the cost of the alloy and raise its melting point whichadversely affects its castability. Therefore, the amounts of rhodium,iridium and rhenium are limited to 5.0 wt % or less each, preferably 3.0wt % or less each. Ruthenium may result in excessively poor castabilityand so is limited to 10.0 wt % or less, preferably 5.0 wt % or less oreven 3.0 wt % or less. In an embodiment one or more of rhodium, iridium,rhenium and ruthenium are absent in the alloy as their presence canhinder recyclability due to difficulty in separating them from platinum.

Tin, indium, gallium: all lower the melting point of pure Ptsignificantly and strongly increase hardness by precipitationstrengthening. However, excessive additions may result in an excessivefraction of intermetallic phases upon cooling of the casting or mayexcessively increase the solidification range. Thus the amount of indiumis limited to 3.0 wt % or less (preferably 2.0 wt % or less or even 1.0wt % or less), and the amount of tin is limited to 3.0 wt % or less(preferably 2.0 wt % or less or even 1.0 wt % or less). The amount ofgallium is limited to 4.0 wt % or less (preferably 3.0 wt % or 2.0 wt %or less). Indium and tin have been found particularly effective and sopreferably indium is present in an amount of 0.5 wt % or more and/or tinis present in an amount of 0.5 wt % or more.

In addition to the ranges in Table 1 the alloys in the invention mayalso contain small amounts of other elements, as incidental impurities.These include titanium, aluminium, chromium, zinc, yttrium, hafnium,zirconium, vanadium, niobium, tantalum, molybdenum, tungsten, silver,scandium, any lanthanide, germanium. Total incidental impurities make up1.0 wt % or less of the alloy, preferably 0.5 wt % or less of the alloy.Any single impurity element is present at a level of 0.5 wt % or less,preferably 0.25 wt % or less or even 0.1 wt % or less. Many of theseelements are highly reactive and may reduce castability and/or lead tothe formation of intermetallic precipitates which in large quantitiescan lead to brittleness and cracking at grain boundaries which reducesductility. In an embodiment aluminium and/or chromium and/or titaniummay be effectively absent.

The second step relies upon thermodynamic calculations used to calculatethe phase diagram and thermodynamic properties for a specific alloycomposition. Often this is referred to as the CALPHAD method(CALculation of PHAse Diagrams).

A third stage involves isolating alloy compositions which have thedesired properties as calculated in the second step. The candidatealloys in the investigated composition space were selected based on thevarious merit indices indicative of the two targets: good castabilityand good mechanical properties.

The merit indices for castability are:

-   -   The melting point index: reflects the melting point of the alloy        which is derivable directly from the thermodynamic calculations.        A lower value is better as a low melting point means metal-mould        reactions can be suppressed, thereby lowering gas porosity and        improving the surface finish. A lower melting point also allows        for a higher superheat relative to one with a higher melting        point. A higher superheat increases fluidity and improves the        form filling characteristics of the alloy.    -   The (equilibrium) solidification range: the range of in which        the alloy would solidify if perfect thermodynamic equilibrium        were maintained throughout. That is, assuming thermodynamic        equilibrium, the temperature where on heating liquid first        appears subtracted from the temperature on heating at which the        last solid melts. This is directly derivable from the        thermodynamic calculations. A larger range is generally        associated with excessive elemental segregation in the as-cast        microstructure which results in poor mechanical properties of        the casting and in increased risk of hot cracking—i.e. crack        formation in the casting during solidification.    -   The hot cracking index: this index more accurately reflects the        risk of hot cracking than the solidification range as the        underlying Scheil model takes into account the segregation        during non-equilibrium solidification conditions encountered in        the vast majority of industrial settings. The larger the value,        the higher the susceptibility to hot cracking. The Scheil model        assumes that as the melt solidifies, the diffusion in it is        infinitely fast and there is no back-diffusion from the already        solidified material. During solidification most alloying        elements in this patent segregate to the remaining liquid phase        (e.g. Ga, Cu . . . ) and lower its melting point. As the        solidification progresses, the liquid becomes more and more        enriched in these elements. If segregation is severe, the last        liquid to solidify can only do so at low temperatures, when        thermal strains in the casting can be high. This can lead to the        formation of cracks as the liquid films between dendrites are        pulled apart and there is not enough liquid remaining to fill        those cracks. This phenomenon is called hot cracking. The hot        cracking index itself is based on the ratio of the temperature        drop required for the last stage of solidification (typically        90% to 99%) and the initial stage of the solidification—from 40%        to 90% solid. These values are taken from the Scheil        solidification curve.    -   The porosity index: the relative change in molar volume of an        alloy between the beginning and the end of Scheil solidification        (i.e. the shrinkage in initial stage of solidification). Larger        thermal strains are more difficult to accommodate, particularly        towards the end of the solidification. If such strains are        excessive, the alloy is at risk of shrinkage porosity which is        undesirable in castings.

The merit indices for mechanical properties are:

-   -   The hardness index: gives the hardness of the as-cast alloy        based on its elemental composition. This index is based on a        statistical analysis of experimental hardness data of a wide        range of platinum alloys available in the literature (Equation        (2)). A higher value is generally better, although hardness        values beyond 220 HV may adversely affect gem setting and so may        not be desirable for certain applications.    -   The phase constitution: the alloys in this invention may form        large volume fractions of brittle intermetallic phases even at        high temperatures at the expense of the ductile platinum gamma        matrix phase (a disordered FCC solid solution phase).        Intermetallic phases are desirable for improving hardness but an        excessively high volume fraction decreases ductility below an        acceptable level. To ensure sufficient ductility, the gamma        fraction merit index is preferably set such that the volume        fraction of the platinum gamma matrix phase is at least 0.3 at        thermodynamic equilibrium at 1000° C.

Using the above described methods in merit indices were calculated for arange of common jewellery alloys shown in Table 2. The relevant propertyvalues predicted by the method for these alloys are shown in Table 3 andwere used as guides for alloy selection.

TABLE 2 List of commonly used Pt-based alloys for jewellery. Pt Au Ga InIr Rh Ru Cu Co Pd Ni Alloy wt % wt % wt % wt % wt % wt % wt % wt % wt %wt % wt % Pt3.5Au1Rh 95.5 3.5 0 0 0 1 0 0 0 0 0 Pt1.5In3Ga 95.5 0 3 1.50 0 0 0 0 0 0 Pt5Ru 95 0 0 0 0 0 5 0 0 0 0 Pt5Ir 95 0 0 0 5 0 0 0 0 0 0Pt5Co 95 0 0 0 0 0 0 0 5 0 0 Pt5Pd 95 0 0 0 0 0 0 0 0 5 0 Pt5Au 95 5 0 00 0 0 0 0 0 0 Pt5Ni 95 0 0 0 0 0 0 0 0 0 5 Pt10Ru 90 0 0 0 0 0 10 0 0 00 Pt10Ir 90 0 0 0 10 0 0 0 0 0 0 Pt3Co7Pd 90 0 0 0 0 0 0 0 3 7 0Pt5Pd5Cu 90 0 0 0 0 0 0 5 0 5 0 Pt3Pd7Cu 90 0 0 0 0 0 0 7 0 3 0 Pt10Pd90 0 0 0 0 0 0 0 0 10 0 Pt10Au 90 10 0 0 0 0 0 0 0 0 0 Pt5Au5Pd 90 5 0 00 0 0 0 0 5 0 Pt10Rh 90 0 0 0 0 10 0 0 0 0 0 Pt15Pd 85 0 0 0 0 0 0 0 015 0 Pt10Pd5Co 85 0 0 0 0 0 0 0 5 10 0 Pt15Ir 85 0 0 0 15 0 0 0 0 0 0

TABLE 3 Property values for most used jewellery alloys, predicted usingthe ABD ® method. Melting Hot Shrinkage in Gamma phase pointSolidification As-cast cracking initial stage of volume Alloy indexrange/° C. hardness/HV index solidification fraction Pt3.5Au1Rh 17.60 20105 2.9 −4.03% 1 Pt1.5In3Ga 16.51 200 231 0.3 −4.27% 0.99 Pt5Ru 17.92 9126 0.4 −3.95% 1 Pt5Ir 17.87 4 92 0.7 −3.87% 1 Pt5Co 17.08 12 153 1.6−4.45% 1 Pt5Pd 17.63 0 73 0.2 −3.99% 1 Pt5Au 17.38 24 120 3.1 −4.10% 1Pt5Ni 16.38 41 145 0.6 −4.15% 1 Pt10Ru 18.55 38 192 0.3 −4.01% 1 Pt10Ir18.09 10 125 0.6 −3.78% 1 Pt3Co7Pd 17.12 16 134 1.8 −4.30% 1 Pt5Pd5Cu17.30 17 144 3.0 −4.23% 1 Pt3Pd7Cu 17.16 30 168 2.4 −4.35% 1 Pt10Pd17.56 1 85 0.2 −4.00% 1 Pt10Au 17.09 58 179 5.4 −4.22% 1 Pt5Au5Pd 17.3616 132 3.1 −4.09% 1 Pt10Rh 18.55 12 94 1.1 −3.61% 1 Pt15Pd 17.47 1 97.50.2 −4.01% 1 Pt10Pd5Co 16.70 25 178.45 1.6 −4.45% 1 Pt15Ir 18.33 19 1570.5 −3.69% 1

Table 3 shows that all benchmark alloys except Pt1.5In3Ga and Pt5Ni havea melting point index above 16.6 indicating a high melting point. Highmelt temperatures during casting are known to exacerbate metal-mouldreactions, leading to increased shrinkage and gas porosity, increasedrisk of inclusions and investment cracking and contamination withalloy-mould reaction products. An alloy with a lower melting point alsoallows for a higher superheat relative to one with a higher meltingpoint. A higher superheat increases fluidity and improves the formfilling characteristics of the alloy. A platinum alloy with a lowmelting point is therefore desirable from the point of view ofcastability. Pt1.5In3.0Ga has a large solidification range (due to thehigh level of gallium) as well as a gamma phase fraction of below 1.0,meaning that the possibility of intermetallic phase precipitation isincreased.

No single alloy is the best at everything. For example, the popularPt5Co alloy is known to produce high-quality castings but can be easilymagnetised, which can cause manufacturing problems. Another popularexample is the Pt5Ru alloy which is non-magnetisable but suffers fromcasting porosity and poor form filling. Manufacturers also preferhardness values of at least 175 HV. Apart from Pt1.5In3Ga, none of theother benchmark alloys meeting the 950 Pt hallmark fit this requirementin an as-cast condition. Even for benchmark alloys meeting the 900 Pthallmark, only Pt10Ru and Pt10Au meet the hardness requirement withoutsubsequent post-processing steps (aging or work hardening). FIG. 1 showsthat many Pt alloys meeting the 900 Pt standard with a hardness higherthan all the benchmark alloys exist.

Based on calculations made on a wider range of composition than shown inTable 1, the effect of each of the alloying elements on the variousmerit indices was determined. With this knowledge, the bounds in Table 1were created. For alloys within the composition range in Table 1, thethermodynamic calculations of step 2 were used to calculate the meltingpoints, the solidification range, the hot cracking index, the porosityindex and the phase constitution of thousands of alloy compositionswithin the range. The results were also used in calculating hot crackingindex, porosity and shrinkage.

FIG. 1 plots for thousands of alloy compositions falling throughout therange allowed by Table 1 both the melting point index (x-axis) and thehardness merit index (y-axis). Also plotted on the graph are the alloyswith composition of Table 2 in their relative positions. As can be seen,alloys with a melting point index less than 16 (and thereby withsuperior castability than for those alloys with a melting point index ofgreater than 16) also tend to have a hardness greater than that of themajority of the prior art alloys.

FIG. 1 shows that many Pt alloys with a composition according to Table 1have a melting point comparable to or lower than all the benchmarkalloys, including Pt1.5In3Ga. FIG. 1 also shows that many Pt alloysmeeting the Table 1 composition have a hardness higher than all thebenchmark alloys.

FIG. 2 is a comparison of gamma phase (FCC platinum solid solution)volume fraction and melting point index between the example alloys andbenchmarks. It shows that many alloys with gamma phase volume fractionsas low as 0.3 (and so acceptable ductility) achieve the required meltingpoint index of 16.6.

FIG. 3 shows that for many alloys which achieve a melting point index oflower than 16.6, a hot cracking index of 4.0 or lower is achievable.This area is shown by the cross hatched polygon.

FIG. 4 shows that for alloys with a melting point index of less than16.6, there are several alloys which also achieve a solidification rangeof 200° C. or less. The preferred solidification range of less than 150°C. is shown in cross hatch. Alloys with a solidification range ofgreater than 150° C. have been omitted from this graph.

The alloy selection procedure was based on several guidelines: first,the main metric for improved castability is a low melting point index. Amelting point index of below 16.0 results in an alloy with asignificantly lower melting point than any of the prior art alloys inTable 3. Such a low melting point index is harder to achieve for thehigh platinum containing alloys and for such alloys (i.e. with a Ptcontent of 95.0 wt % or more), the melting point index requirement isrelaxed to 16.6 or less. This is acceptable because for high valuejewellery (i.e. high Pt content), some machining (e.g. polishing) aftercasting is acceptable and there may be more limitations on the alloyingelements which can be used considering potential requirements for highhardness and low solidification range. Second, for improved mechanicalproperties, hardness values should exceed 150 HV but should be tuneableas hardness requirements may vary depending on the application.

On the basis of these results, the following equation was derived whichexpresses the melting point index as a function of composition. Theequation is derived from results of alloys falling within the range ofTable 1. Therefore, for a platinum alloy falling within thecompositional range of Table 1 and in which equation (1) below is 16.0or less, such an alloy will have superior castability compared to theprior art alloys of Table 2 and will also likely have higher hardness.For an alloy with a platinum content of 95.0 wt % or more and for whichequation (1) below gives a value of 16.6 or less (or even 16.4 or lessor 16.2 or less (all of the example alloys of the invention in Table 4meet this harshest criterion)), the castability will be improvedcompared to all of the prior art alloys of Table 2 with a similar highplatinum composition except Pt1.5In3.0Ga and Pt5Ni. However, thesealloys suffer from very high solidification range (due to excessive Ga)and low hardness, respectively.

−0.1028*W _(Co)−0.1201*W _(Cu)−0.2113*W _(Fe)−0.3368*W _(Ga)−0.1125*W_(In)−0.1639*W _(Ni)−0.015*W _(Pd)−0.1959*W _(Sn)+17.276261−0.20*W_(Mn)+0.0678*W _(Ru)+0.035*W _(Ir)+0.045*W _(Rh)−0.059*W _(Au)+0.066*W_(Re)   (1)

in which W_(Co), W_(Cu), W_(Fe), W_(Ga), W_(In), W_(Ni), W_(Pd), W_(Sn),W_(Mn), W_(Ru), W_(Ir), W_(Rh), W_(Au) and W_(Re) are the weight percentof cobalt, copper, iron, gallium, indium, nickel, palladium, tin,manganese, ruthenium, iridium, rhodium, gold and rhenium in the alloyrespectively.

Alloy compositions exist within the range of Table 1 with an even highermelting point index. Preferably irrespective of the platinum content ofthe alloy, equation (1) is 16.0 or less. Alloys with lower values ofequation (1) are preferred, particularly those in which equation (1) is15.5 or less, more preferably 15.0 or less and most preferably 14.5 orless.

The hardness of a platinum alloy can be approximated according to thefollowing equation (2) based on experimental results:

60+W _(Pd)*2.5+W _(Rh)*3.4+W _(Ir)*6.455+W _(Au)*11.93+W _(Ru)*13.241+W_(Cu)*14.328+W _(Re)*16.6+W _(In)*16.9+W _(Mn)*18.48+W _(Co)*18.69+W_(Fe)*21.879+W _(In)*29+W _(Sn)*28.207+W _(Ga)*42.379   (2)

in which W_(Co), W_(Cu), W_(Fe), W_(Ga), W_(In), W_(Ni), W_(Pd), W_(Sn),W_(Rh), W_(Ir), W_(Au), W_(Ru), W_(Re), and W_(Mn) are the weightpercent of cobalt, copper, iron, gallium, indium, nickel, palladium,tin, rhodium, iridium, gold, ruthenium, rhenium, and manganese in thealloy respectively.

If equation (2) is greater than or equal to 150 (as is achievable byalloys of the present invention as shown in Table 5 below), the hardnessof the platinum alloy will be acceptable. Preferably, equation (2) isgreater than or equal to 200, preferably 225, more preferably 250, evenmore preferably 275 or most preferably 300, in which case an alloy witha correspondingly increased hardness results and this may be preferredfor certain applications. Those skilled in the art of jewellery knowhardness should be high enough to improve wear resistance, andfacilitate gem setting as well as polishing, but if hardness is toohigh, softer gemstones risk getting damaged during setting. Thecomposition space allows a wide hardness range and alloys in theinvention have a hardness of at least 150 HV. When setting hardgemstones such as diamonds or making gemstone-free jewellery, harderalloys may be preferred. In some embodiments lower hardness is preferred(for example to facilitate gem setting), so that preferably equation (2)is less than or equal to 280, more preferably less than or equal to 260,and most preferably less than or equal to 240.

Solidification range: excessive range often results in solidificationdefects. The alloy preferably has a solidification range of less than200° C., preferably the alloy composition has a solidification range of150° C. or less. More preferably wherein the alloy composition has asolidification range of 125° C. or less, more preferably wherein thealloy composition has a solidification range of 100° C. or less, evenmore preferably wherein the alloy composition has a solidification rangeof 75° C. or less, most preferably wherein the alloy composition has asolidification range of 50° C. or less. The inventors have foundensuring that the following equation is satisfied: 0.35 W_(Au)+0.6W_(Sn)+0.6 W_(In)+W_(Ga)≤3.75 helps to produce an alloy with a lowersolidification range. Preferably 0.35 W_(Au)+0.6 W_(Sn)+0.6W_(In)+W_(Ga)≤3.0. As described below, equation (4) must be fulfilled sothat the desired melting point can be achieved without increasing thesolidification range excessively. The complicated interaction betweenelements means that it has not been possible for the inventors to derivean accurate equation using simple ratios of all the elements in Table 1defining the solidification range from the thermodynamic data. However,solidification range can be measured experimentally by differentialscanning calorimetry. The difference (in Kelvin) between the onset andend of the exothermic peak associated with the phase transition fromliquid to solid upon slow cooling (at the rate of 10 K/min or less) isdefined as the solidification range. The below Table gives thesolidification range of various binary Pt alloys at 95 wt % Pt and showsthe relative effects of a selection of alloying elements from which theskilled person can see which elements are most likely to increase thesolidification range. Note, however, that the values in the Table werederived from binary phase diagrams of those elements with platinum—theyrepresent solidification ranges when the system is near thermodynamicequilibrium throughout solidification. Because of kinetic effects,however, solidification ranges measured experimentally are always largerthan equilibrium ranges.

Element Ni Cr Pd Sn Co Fe Cu Ru Rh Ir Au In Ga Al Re Mn TiSolidification range of 42 0.2 0.3 153 12 16 16 9 11 4 24 151 241* 15*10 147 110* Pt with 5 wt % of element (in Kelvin) *forms phases otherthan gamma upon solidification

In an embodiment, the alloy consists, in weight percent, of: 0.0 to 5.0cobalt, 0.0 to 10.0 copper, 0.0 to 7.0 iron, 0.0 to 4.0 gallium, 0.0 to3.0 indium, 0.0 to 7.0 nickel, 0.0 to 15.0 palladium, 0.0 to 3.0 tin,85.0 or more platinum and incidental impurities. Such alloys arepreferred because gold and manganese have low effect on melting pointand hardness, but increase the solidification range and iridium,rhenium, rhodium and ruthenium tend to increase the melting point. Thusadditions of those elements are not as powerful as additions of theother elements and so their use is less preferred, given the low amountsof alloying element which can be used (in order to keep the platinumcontent high to meet hallmarking requirements). However, a small amount(up to 1.0 weight percent in sum) of the elements gold, iridium,manganese, rhenium, rhodium, and ruthenium can be contained in such analloy.

The following equation (3) was derived which expresses thesolidification range index as a function of composition and is valid foralloys falling within the range of Table 1.

0.041W _(Au) W _(Co)+0.122W _(Au) W _(In)−1.96W _(Au) W _(Ni)+1.87W_(Au) W _(Sn)+0.903W _(Au) ²+1.74W _(Co) W _(Ga)+13.4W _(Co) W_(In)+1.24W _(Co) W _(Mn)+5.04W _(Co) W _(Sn)+1.02W _(Co) ²+8.97W _(Cu)W _(Fe)+1.74W _(Cu) W _(Ga)+4.38W _(Cu) W _(In)+1.16W _(Cu) W_(Mn)+0.491W _(Cu) W _(Ni)+3.69W _(Cu) W _(Sn)+0.22W _(Cu) ²+1.68W _(Fe)W _(Ga)+3.31W _(Fe) W _(In)−1.26W _(Fe) W _(Mn)+5.07W _(Fe) W_(Sn)+0.199W _(Fe) ²+5.35W _(Ga) W _(In)+0.086W _(Ga) W _(Mn)+3.27W_(Ga) W _(Re)+33.3W _(Ga) W _(Rh)+4.56W _(Ga) W _(Ru)+2.21W _(Ga) W_(Sn)+29.0W _(Ga)+8.49W _(Ga) ²+9.09W _(In) W _(Mn)−0.28W _(In) W_(Ni)+15.4W _(In) W _(Rh)+0.992W _(In) W _(Ru)+11.7W _(In)+6.68W _(In)²+0.863W _(Ir) ²+5.73W _(Mn) W _(Ni)−0.02W _(Mn) W _(Ru)+5.68W _(Mn) W_(Sn)+18.4W _(Mn)−0.89W _(Mn) ²+0.49W _(Ni) W _(Ru)+0.186W _(Ni) ²+4.48W_(Re) W _(Sn)+1.15W _(Re) ²−5.11W _(Rh) W _(Sn)+2.04W _(Rh) ²+0.885W_(Ru) W _(Sn)+1.28W _(Ru) ²+1.58W _(Sn)+9.49W _(Sn) ²+11.6   (3)

in which W_(Co), W_(Cu), W_(Fe), W_(Ga), W_(In), W_(Ni), W_(Pd), W_(Sn),W_(Mn), W_(Ru), W_(Ir), W_(Rh), W_(Au) and W_(Re) are the weight percentof cobalt, copper, iron, gallium, indium, nickel, palladium, tin,manganese, ruthenium, iridium, rhodium, gold and rhenium in the alloyrespectively. Preferably the value of equation (3) is equal to or lessthan 140. Such an alloy has improved castability due to lowersolidification range. Preferably the value of equation (3) is equal toor less than 120 or even equal to or less than 100, or even equal to orless than 80 and most preferably equal to or less than 60.

The alloys in the invention are characterised by a combination ofsufficient hardness as well as a narrow solidification range and a lowmelting point, whose combination leads to good castability. Two distinctgroups of alloying elements can be identified: those which improvecastability by lowering the melting point and not excessively increasingthe solidification range (Ni, Co, Fe, Pd and Cu) and those whichincrease hardness and decrease the melting point but decreasecastability by increasing the solidification range (Sn, In, Ga). Thealloys in the invention need at least one of the elements from eachgroup in order to satisfy both criteria according to equations

W _(Co) +W _(Pd) +W _(Fe) +W _(Ni) +W _(Cu)≥1.0   (4)

W _(Sn) +W _(In) +W _(Ga)≥0.25   (5)

Preferably W_(Co)+W_(Pd)+W_(Fe)+W_(Ni)+W_(Cu)≥2.0 as such an alloy haslower melting point without a large increase in solidification range.

It was also found that having two or more elements from the group of Sn,In and Ga is beneficial in reducing the amount of intermetallic phasesformed in interdendritic regions in the last stages of solidification(‘terminal intermetallics’). Because of their brittleness and coarsemorphology, terminal intermetallics reduce the ductility of castings andadversely affect subsequent forming and machining. Their fraction shouldtherefore be reduced. FIG. 5 shows the variation in the fraction ofterminal intermetallics in a platinum alloy containing 5 wt % Co, 2 wt %Fe and 4.9 wt % of any combination of Ga, In and Sn. The effect ofreduced intermetallics is noticeable even with additions of a secondalloying element in small amounts, including as little as 0.1 wt %(which is quite a large fraction of the minimum of the sum of thoseelements being 0.25 wt %) and so there is a requirement of the alloy tohave two or more of gallium, indium and tin present in an amount of 0.1wt % or more, preferably 0.25 wt % or more, even more preferably 0.5 wt% or more.

As can be seen from FIG. 5 , the lowest fraction of terminalintermetallics is achieved when all three elements are present. While itis true that using pure Sn or In yields less terminal intermetallicsthan using a combination of three elements when the fraction of Gaexceeds about 0.4, a high Ga content may be desirable for otherreasons—for example to achieve a very high hardness. In this case,replacing some Ga with In or Sn will only somewhat reduce hardness butcould appreciably reduce the fraction of terminal intermetallics. Whileone can use a combination of Ga and In or Ga and Sn to achieve a desiredhardness, using all three elements will, at the same time, reduce thefraction of terminal intermetallics may therefore be preferable.

It is expected that using more than one of In, Ga or Sn to reduce thefraction of terminal intermetallics holds more generally for the alloysin this invention. The underlying physical reason is likely that for agiven weight percent of alloying elements (e.g. 10%), solid solution isthermodynamically more favourable when the number of alloying elementsincreases.

As can be seen, alloys with indium and tin, of the group of gallium,indium and tin, two of which are compulsory, have lower levels ofterminal intermetallics than alloys without those two elements.Therefore preferably indium and tin are the two elements of gallium,indium and tin which are present, where reduced intermetallicprecipitation is preferred over other properties.

By mixing the elements of gallium, indium and tin present in amountsclose to being equal, the amount of intermetallic can be reducedcompared to the case where only small amounts of the second or third ofthose three elements are present. Thus in the case that the two or moreof gallium, indium and tin are indium and gallium, preferably thefollowing equation is satisfied in which W_(Ga) and W_(In), are theweight percent of gallium and indium in the alloy

0.5W_(In)≤W_(Ga)≤1.5W_(In).

In the case that the two or more of gallium, indium and tin are tin andgallium preferably the following equation is satisfied in which W_(Ga)and W_(Sn), are the weight percent of gallium and tin in the alloy

0.5W_(Sn)≤W_(Ga)≤1.5W_(Sn).

In the case that the two or more of gallium, indium and tin are indiumand tin preferably the following equation is satisfied in which W_(In),and W_(Sn), are the weight percent of indium and tin in the alloy

0.5W_(In)≤W_(Sn)≤1.5W_(In).

In the case that the two or more of gallium, indium and tin are indium,tin and gallium preferably the following equations are satisfied inwhich W_(Ga), W_(In), and W_(Sn), are the weight percent of gallium,indium and tin in the alloy

0.3W_(In)≤W_(Ga)≤1.3W_(In)

0.3W_(Sn)≤W_(Ga)≤1.3W_(Sn)

0.3W_(In)≤W_(Sn)≤1.3W_(In).

Hot cracking: excessive values often result in solidification defects,particularly cracking. The Pt10Au benchmark alloy has the largest indexvalue yet it is not excessively prone to cracking during solidification.Hot cracking index was therefore limited to somewhat less than the hotcracking value of Pt10Au. The following equation (6) was derived whichexpresses the hot cracking index as a function of composition. Theequation is derived from results of alloys falling within the range ofTable 1. Therefore, for a platinum alloy falling within thecompositional range of Table 1 and in which equation (6) below is 4.0 orless, such an alloy will have superior castability compared to Pt10Au.Preferably the hot cracking index of equation 3 is 3.941 or less. Allexamples of the invention in Table 4 fall within that range.

−0.1*W _(Co)−0.4933*W _(Cu)−0.32*W _(Fe)−1.16377*W _(Ga)−0.54278*W_(In)−0.08612*W _(Ni)+0.06915*W _(Pd)−0.69928*W _(Sn)+4.169+0.04*W_(Mn)+0.133*W _(Au)   (6)

wherein W_(Co), W_(Cu), W_(Fe), W_(Ga), W_(In), W_(Ni), W_(Pd), W_(Sn),W_(Mn) and W_(Au) are the weight percent of cobalt, copper, iron,gallium, indium, nickel, palladium, tin, manganese and gold in the alloyrespectively.

Even more preferably, the hot cracking index is 3.5 or less, or even 3.0or less, or even 2.5 or less. Thus equation (6) is preferably 3.5 orless, or even 3.0 or less or most preferably 2.5 or less.

Many alloying elements which were investigated, particularly somefirst-row transition metals (e.g. Fe) and some p-block elements (e.g.Ga, Sn), may form large quantities of intermetallic precipitates whichcan reduce ductility. In nickel superalloys which are metallurgicallysimilar, the maximum allowable precipitate volume fraction is some 0.7,ensuring there is enough ductile matrix phase to prevent brittleness.Based on this insight, the minimum equilibrium volume fraction of theductile gamma matrix phase at 1000° C. is desirably 0.3, which isachieved by many of the examples. Preferably the alloy compositioncomprises 0.55 or more volume fraction gamma phase at 1000° C.,preferably 0.6 or more volume fraction gamma phase, more preferably 0.7or more volume fraction gamma phase, even more preferably 0.8 or morevolume fraction gamma phase, most preferably 0.9 or more volume fractiongamma phase. Results of thermodynamic calculations have not allowed asimple equation to be derived which predicts the volume fraction gammaprime based on the composition. However, composition can be determinedexperimentally by the following method. After a substantially longthermal exposure (for example 200 h) at 1000° C. the specimen isquenched in water, a section is taken through the material and polishedusing conventional/standard metallurgical preparation techniques forscanning electron microscopy. Once prepared, the microstructure shouldbe observed in a scanning electron microscope. A minimum of 10 imagesshould be taken which provide a statistically representative dataset.The images should cover an area of at least 1 mm². The 2-dimensionalimages which reveal the microstructure, should be processed to identifyall the precipitate particles larger than 30 nm, and their area fractionshould be measured. Their combined area fraction is complementary to thefraction of the gamma matrix phase with the relationship M=1−P, where Pis the volume fraction of precipitate phases and M is the volumefraction of the gamma matrix phase. The measured area fractionscorrespond directly to volume fractions.

The formation of intermetallic ordered phases directly from the meltproduces large brittle grains which severely reduce ductility. Tofurther ensure sufficient ductility, the alloys preferably are thosewhich first form gamma phase on cooling from liquid. In the gamma phaseall alloying elements are in solid solution. This can be determinedexperimentally by following the procedure similar to the one in theparagraph above. The procedure is modified by instead measuring the areafraction of any simple polygonal precipitates whose orientation israndom and whose largest diameter exceeds 0.2 mm. If their area fractionexceeds 0.025, this is indicative of excessive intermetallicprecipitation directly from the melt.

In an embodiment the condition 2.5 W_(Ir+)3 W_(Ru)≤7.5 is preferably metin order to achieve a low melting point.

The results show that if the following Equation 5 is satisfied, that alower melting temperature and a narrow solidification range of can beachieved in which W_(Co), W_(Fe), W_(Ni), and W_(Pd) are the weightpercent of cobalt, iron, nickel, and palladium in the alloyrespectively. This is particularly the case when other alloying elementsare present in small amounts or are absent.

(W _(Co) +W _(Pd))/11+(W _(Fe) +W _(Ni))/2.2≥1.0   (7)

In an embodiment the alloy consists of platinum, cobalt, iron, nickeland palladium, with any other elements being present in a sum amount of1.0 wt % or less (preferably 0.5 wt % or less) and any individual otherelement present in an amount of 0.5 wt % or less (preferably 0.25 wt %or less). This is advantageous because Fe and Ni lower the melting pointmore effectively than Co and Pd so more of the latter is needed toachieve the same effect.

The most favourable combination of properties have been found when thefollowing equation in which W_(Co), W_(Fe), and W_(Ni), are the weightpercent of cobalt, iron, and nickel in the alloy is satisfied3.0≤W_(Co)+W_(Fe)+W_(Ni)≤4.5, particularly in the absence of copper andpalladium. Such an alloy has reduced melting point without acorresponding increase in solidification range. Additionally oralternatively a good combination of properties is achieved when thefollowing equation in which W_(Ga), W_(In), and W_(Sn), are the weightpercent of gallium, indium and tin in the alloy is fulfilled0.4≤W_(Ga)+W_(In)+W_(Sn)≤2.2. This gives an alloy with superior hardnesswith a limited corresponding increase in solidification range. In anembodiment the platinum alloy composition is made up of 95 weightpercent or more of platinum and satisfies the following equation inwhich W_(Co), W_(Fe), and W_(Ni), are the weight percent of cobalt,iron, and nickel in the alloy 3.0≤W_(Co)+W_(Fe)+W_(Ni)≤4.5 as well asthe following equation in which W_(Ga), and W_(Sn), are the weightpercent of gallium, indium and tin in the alloy0.4≤W_(Ga)+W_(In)+W_(Sn)≤2.2. Such an alloy has a good balance ofcastability and hardness while still meeting the 950 platinumhallmarking requirements.

Table 4 gives several example alloy compositions which fall within thepresent invention. That is, all alloy compositions fall within the rangeof compositions of Table 1. All values are in weight percent.

TABLE 4 Alloy Pt Au Co Cu Fe Ga In Ir Mn Ni Pd Re Rh Ru Sn Example 1 950 0 0 2 2.5 0 0 0 0 0 0 0 0 0.5 Example 2 96.25 0 0 0 2 1.5 0 0 0 0 0 00 0 0.25 Example 3 96 0 0 0 2 0 1.5 0 0 0 0 0 0 0 0.5 Example 4 95.5 0 00 2 1 1.5 0 0 0 0 0 0 0 0 Example 5 95.5 0 0 0 2 2 0.5 0 0 0 0 0 0 0 0Example 6 94.5 0 0 0 2 2 0.5 0 0 0 0 0 0 0 1 Example 7 96 0 0 0 2 0 0.50 0 0 0 0 0 0 1.5 Example 8 95.25 0 0 0 2 2.5 0 0 0 0 0 0 0 0 0.25Example 9 93.25 0 0 0 5 0.5 0 0 0 0 0 0 0 0 1.25 Example 10 91.75 0 0 06 1 0 0 0 0 0 0 0 0 1.25 Example 11 93.25 0 0 0 5 0 0.25 0 0 0 0 0 0 01.5 Example 12 92.75 0 0 0 2.5 1 0 0 0 2.5 0 0 0 0 1.25 Example 13 92.750 0 0 0 1 0 0 0 5 0 0 0 0 1.25 Example 14 92.75 0 0 2.5 2.5 1 0 0 0 0 00 0 0 1.25 Example 15 91.75 0 0 5 1 1 0 0 0 0 0 0 0 0 1.25 Example 1692.75 0 2.5 0 2.5 1 0 0 0 0 0 0 0 0 1.25 Example 17 91.25 0 5 0 2 1 0 00 0 0 0 0 0 0.75 Example 18 94.75 0 0 0 2.5 2.5 0.25 0 0 0 0 0 0 0 0Example 19 95 0 0 0 2 2.5 0 0 0 0 0 0 0 0 0.5 Example 20 85 0 0 0 5 2.50.5 0 0 0 7 0 0 0 0 Example 21 88 2 3 0 2 0.5 3 0 0 1.5 0 0 0 0 0Example 22 87.25 9 0 0 3 0.25 0.5 0 0 0 0 0 0 0 0 Example 23 90 0 1.51.5 3 1 0 2.5 0 0 0 0 0 0 0.5 Example 24 89.5 0 0 0 1.5 2.5 1 0 0 0 3 00 1.5 1 Example 25 88.5 0 3 0 0 2 0 0 0 3 0 0 0 3 0.5 Example 26 89 01.5 0 4 1 1 0 0 0 3 0 0 0 0.5 Example 27 90.5 0 0 0 4.5 0 1 0 0 0 3 0 00 1 Example 28 89 0 2 0 1.5 1.5 0 0 0 1.5 0 0 2.5 0 2 Example 29 90.75 00 0 3 0.25 2 0 0 2 0 0 0 1 1 Example 30 90.5 0 0 0 4.5 1 1 0 0 0 3 0 0 00 Example 31 90 2.5 0 0 4.5 1 0.5 0 0 0 0 0 0 1.5 0 Example 32 90.75 2.50 0 4.5 0 0.25 0 0 1.5 0 0 0 0 0.5 Example 33 89.75 0 1.5 0 4.5 0.5 0.252 0 1.5 0 0 0 0 0 Example 34 87.75 0 1.5 0 4.5 0 0.25 0 0 0 0 0 4 0 2Example 35 85 0 0 0 7 0.5 0.5 0 0 5 0 2 0 0 0 Example 36 87.5 0 0 0 70.25 0.25 0 5 0 0 0 0 0 0 Example 37 86.5 0 0 0 7 0.5 0 0 0 0 0 1 2 0 3Example 38 88.5 0 0 0 5 0.25 0.25 0 2.5 0 0 1 0 2.5 0 Example 39 85.25 00 0 3 2.5 0.25 0 2.5 0 0 4 0 2.5 0 Example 40 85.75 0 0 0 5 3 0.5 0 2.52 0 1 0 0 0.25 Example 41 89.25 0 0 0 5 0.25 0.25 0 5 0 0 0 0 0 0.25Example 42 85 0 0 0 4 0 3 0 0 0 0 0 0 5 3 Example 43 85 0 0 0 2 2 0 0 00 10.5 0 0 0 0.5 Example 44 85 0 0 0 0 2.5 0 0 0 0 11 0 0 0 1.5 Example45 85 0 0 0 1 1 1 0 9 1 0 0 0 0 2 Example 46 89 0 0 9 0 1 1 0 0 0 0 0 00 0 Example 47 95.22 0 0 0 3 0 0.25 0 0 1.28 0 0 0 0 0.25 Example 4895.08 0 0 0 3.55 0 0.23 0 0 0.89 0 0 0 0 0.25 Example 49 95.19 0 0 03.92 0.15 0.74 0 0 0 0 0 0 0 0 Example 50 95.19 0 0 0 4.13 0.53 0.15 0 00 0 0 0 0 0 Example 51 95.12 0 0.85 0 3 0.45 0 0 0 0.43 0 0 0 0 0.15Example 52 95 0 0 0 2.7 0.45 0 0 0 1.7 0 0 0 0 0.15 Example 53 95.21 00.89 0 3.4 0.15 0.25 0 0 0 0 0 0 0 0.1 Example 54 95.13 0 0 0 2.3 0.250.2 0 0 2.12 0 0 0 0 0 Example 56 95.07 0 0.82 0 3.24 0 0.21 0 0 0.41 00 0 0 0.25 Example 57 95.1 0 1.7 0 2.7 0.35 0.15 0 0 0 0 0 0 0 0 Example58 95.06 0 0 0 2.9 0.35 0.1 0 0 1.34 0 0 0 0 0.25 Example 59 95.07 00.85 0 2.4 0.2 0.2 0 0 1.28 0 0 0 0 0 Example 60 95.38 0 0 0 2.7 0.20.22 0 0 1.28 0 0 0 0 0.22 Example 62 95.18 0 0 0 3.39 1.28 0.15 0 0 0 00 0 0 0 Example 63 95.07 0 0 0 1.75 0.4 0.25 0 0 2.43 0 0 0 0 0.1Example 64 95.18 0 0.94 0 3.26 0.47 0 0 0 0 0 0 0 0 0.15 Example 6595.06 0 2.54 0 1.7 0.3 0.15 0 0 0 0 0 0 0 0.25 Example 67 95.18 0 0 02.33 0.47 0.15 0 0 1.87 0 0 0 0 0 Example 70 95.18 0 0 0 0.85 0.43 0.150 0 3.39 0 0 0 0 0 Example 74 95.18 0 1.7 0 0 0.43 0 0 0 2.54 0 0 0 00.15 Example 75 95.19 0 0 0 0 0.94 0 0 0 3.72 0 0 0 0 0.15 Example 7795.18 0 0.89 0 3.11 0 0.67 0 0 0 0 0 0 0 0.15 Old example 51 95.33 0 0 03.92 0 0.5 0 0 0 0 0 0 0 0.25 Old example 56 95.31 0 0 0 2.97 0 0.22 0 01.28 0 0 0 0 0.22 Old example 57 95.33 0 0 0 0 0.89 0 0 0 3.55 0 0 0 00.23 Old example 62 95.32 0 0 0 3.11 1.34 0.23 0 0 0 0 0 0 0 0 Oldexample 64 95.31 0 0.82 0 2.84 0 0.41 0 0 0.41 0 0 0 0 0.21 Old example65 95.33 0 0 0 2.66 1.34 0.67 0 0 0 0 0 0 0 0 Old example 67 95.33 0 0 02.97 0.85 0 0 0 0 0 0 0 0 0.85 Old example 68 95.32 0 0 0 0.82 0 0.21 00 3.24 0 0 0 0 0.41 Old example 69 95.32 0 0.82 0 0 0.41 0 0 0 3.24 0 00 0 0.21 Old example 72 95.33 0 0 0 0 0 0.64 0 0 3.39 0 0 0 0 0.64 Oldexample 74 95.32 0 0.89 0 0 0.45 0.23 0 0 2.22 0 0 0 0 0.89 Example 095.288 0 0 0 0 0 0.653 0 0 3.405 0 0 0 0 0.654 Comparative 95.41 0 4.590 0 0 0 0 0 0 0 0 0 0 0 example 1 Comparative 96.33 0 0 0 0 0 0 0 0 0 00 0 3.67 0 example 2 Comparative 95.62 0 0 0 0 2.95 1.43 0 0 0 0 0 0 0 0example 3

Table 5 shows the main properties achieved by these examples, namelygamma fraction as predicted by the thermodynamic model, hardness aspredicted by the above-mentioned equation, hot cracking index asindicated by the abovementioned fit, melting point index as obtained bythe above-mentioned fit, and solidification range as measured by thethermodynamic model. As can be seen, the hot cracking index of the rangeof alloys compares favourably to the hot cracking index of many of theprior art alloys. Although the thermodynamic calculations indicate thatsome alloys have high gamma fraction and the hardness predicationindicates that such alloys have high hardness, it is thought that thisis due to the formation of precipitates below 1000° C.

TABLE 5 Hot Melting Gamma W_(Ga) + 0.6 W_(In) + W_(In) + W_(Co) +W_(Pd) + cracking point index fraction at 0.6 W_(Sn) + W_(Ga)+ W_(Fe) +W_(Ni) + Alloy (fit) (fit) 1000° C. Hardness Equation 3 0.35 W_(Au)W_(Sn) W_(Cu) Example 1 0.27 15.9 0.943 223.8 143.1 2.8 3 2 Example 21.61 16.3 0.989 174.4 100.9 1.65 1.75 2 Example 3 2.37 16.6 0.995 161.467.5 1.2 2 2 Example 4 1.55 16.3 0.986 189.6 96.7 1.9 2.5 2 Example 50.93 16.1 0.984 203.0 118.8 2.3 2.5 2 Example 6 0.23 15.9 0.982 231.2138.9 2.9 3.5 2 Example 7 2.21 16.5 0.999 160.6 78.7 1.2 2 2 Example 80.44 16.0 0.954 216.8 138.5 2.65 2.75 2 Example 9 1.11 15.8 0.292 225.8110.0 1.25 1.75 5 Example 10 0.21 15.4 0.000 268.9 143.1 1.75 2.25 6Example 11 1.38 15.9 0.191 219.0 99.7 1.05 1.75 5 Example 12 1.12 15.80.949 234.6 117.9 1.75 2.25 5 Example 13 1.70 15.9 1.000 222.1 110.81.75 2.25 5 Example 14 0.10 15.9 0.995 228.2 184.0 1.75 2.25 5 Example15 −0.66 15.9 1.000 231.2 183.6 1.75 2.25 6 Example 16 1.08 15.9 0.936239.1 138.3 1.75 2.25 5 Example 17 1.34 15.9 0.986 260.7 141.3 1.45 1.757 Example 18 0.32 15.9 0.836 227.9 140.0 2.65 2.75 2.5 Example 19 0.2715.9 0.943 223.8 143.1 2.8 3 2 Example 20 −0.13 15.2 0.890 307.3 197.22.8 3 12 Example 21 1.16 15.7 0.988 317.2 225.6 3 3.5 6.5 Example 223.84 16.0 0.846 258.1 55.4 3.7 0.75 3 Example 23 0.81 16.0 0.991 247.8149.9 1.3 1.5 6 Example 24 −0.26 15.9 0.942 283.3 185.4 3.7 4.5 4.5Example 25 0.93 15.9 1.000 305.4 161.6 2.3 2.5 6 Example 26 0.89 15.70.929 268.5 128.9 1.9 2.5 8.5 Example 27 1.69 16.0 0.765 223.2 68.2 1.22 7.5 Example 28 0.22 15.7 1.000 284.0 186.9 2.7 3.5 5 Example 29 0.9615.9 0.933 269.5 120.9 2.05 3.25 5 Example 30 1.23 15.8 0.846 237.3 98.01.6 2 7.5 Example 31 1.63 15.9 0.733 265.0 93.3 2.175 1.5 4.5 Example 322.45 15.8 0.713 235.0 57.9 1.325 0.75 6 Example 33 1.73 15.8 0.850 253.275.3 0.65 0.75 7.5 Example 34 1.04 15.9 0.846 263.8 139.0 1.35 2.25 6Example 35 0.65 14.9 0.994 366.5 79.7 0.8 1 12 Example 36 1.70 14.71.000 323.4 65.2 0.4 0.5 7 Example 37 −0.75 15.2 0.000 342.4 234.5 2.33.5 7 Example 38 2.24 15.8 0.967 283.1 58.4 0.4 0.5 5 Example 39 0.2615.7 0.868 384.5 144.3 2.65 2.75 3 Example 40 −1.44 14.3 0.992 414.7211.8 3.45 3.75 7 Example 41 2.17 15.1 1.000 286.7 65.2 0.55 0.75 5Example 42 −0.84 15.8 0.332 385.3 239.7 3.6 6 4 Example 43 1.58 15.91.000 228.9 162.3 2.3 2.5 12.5 Example 44 0.97 16.0 1.000 235.8 228.63.4 4 11 Example 45 1.02 14.3 1.000 392.9 135.2 2.8 4 2 Example 46 −1.9815.7 1.000 260.3 173.6 1.6 2 9 Example 47 2.79 16.4 0.892 161.6 47.3 0.30.5 4.28 Example 48 2.66 16.3 0.793 166.4 48.5 0.288 0.48 4.44 Example49 2.34 16.3 0.664 173.6 56.7 0.594 0.89 3.92 Example 50 2.15 16.2 0.635177.2 67.4 0.62 0.68 4.13 Example 51 2.46 16.3 0.861 172.1 65.2 0.54 0.64.28 Example 52 2.53 16.2 0.931 171.1 62.3 0.54 0.6 4.4 Example 53 2.6116.4 0.753 167.5 55.2 0.36 0.5 4.29 Example 54 2.85 16.3 0.980 162.552.0 0.37 0.45 4.42 Example 56 2.73 16.4 0.815 166.3 50.8 0.276 0.464.47 Example 57 2.65 16.4 0.882 170.0 61.6 0.44 0.5 4.4 Example 58 2.4916.3 0.904 170.9 61.2 0.56 0.7 4.24 Example 59 2.86 16.4 0.958 164.352.2 0.32 0.4 4.53 Example 60 2.69 16.4 0.932 161.8 54.6 0.464 0.64 3.98Example 62 1.51 16.1 0.825 192.8 96.3 1.37 1.43 3.39 Example 63 2.7316.3 1.000 166.4 60.5 0.61 0.75 4.18 Example 64 2.38 16.3 0.793 173.067.1 0.56 0.62 4.2 Example 65 2.77 16.5 1.000 168.8 67.8 0.54 0.7 4.24Example 67 2.63 16.3 0.973 166.8 61.1 0.56 0.62 4.2 Example 70 3.02 16.41.000 158.5 59.6 0.52 0.58 4.24 Example 74 3.17 16.5 1.000 157.2 63.60.52 0.58 4.24 Example 75 2.65 16.3 1.000 166.9 81.9 1.03 1.09 3.72Example 77 2.62 16.4 0.818 168.3 56.5 0.492 0.82 4 Old example 51 2.4716.3 0.645 167.3 52.8 0.45 0.75 3.92 Old example 56 2.84 16.4 0.898159.2 46.3 0.264 0.44 4.25 Old example 57 2.67 16.3 1.000 164.2 80.31.028 1.12 3.55 Old example 62 1.49 16.1 0.863 191.5 97.8 1.478 1.573.11 Old example 64 2.77 16.4 0.886 162.2 52.1 0.372 0.62 4.07 Oldexample 65 1.39 16.2 0.920 194.4 99.5 1.742 2.01 2.66 Old example 671.64 16.2 0.874 185.0 95.5 1.36 1.7 2.97 Old example 68 3.23 16.5 1.000150.4 47.4 0.372 0.62 4.06 Old example 69 3.18 16.5 1.000 153.4 61.70.536 0.62 4.06 Old example 72 3.08 16.5 1.000 153.9 57.0 0.768 1.283.39 Old example 74 2.62 16.5 1.000 165.0 79.1 1.122 1.57 3.11 Example 03.06 16.5 1.000 154.9 57.5 0.7842 1.307 3.405 Comparative 3.71 16.81.000 145.8 49.1 0 0 4.59 example 1 Comparative 4.17 17.5 1.000 108.640.0 0 0 0 example 2 Comparative −0.04 16.1 1.000 226.5 146.9 3.808 4.380 example 3

As can be seen from Table 3, achieving low melting temperature in aplatinum alloy is difficult with the presence of only one of thecommonly used alloying elements. As shown in Tables 4 and 5, theexamples of the present invention achieve the desired low melting pointand high hardness by incorporating two or more, preferably three or moreof the gallium, indium and tin and one or more of cobalt, palladium,iron, nickel and copper.

EXAMPLES AND COMPARATIVE EXAMPLES

Casting trials demonstrated that examples from this invention (Example0) indeed have a better combination of castability and hardness thanComparative examples 1 to 3. The alloys were investment cast intopreheated ceramic moulds. The shape of the castings is shown in FIG. 6 .Parts of this tree were then used to evaluate the form-filling capacityof the alloys Vickers hardness and porosity. As an indicator of theform-filling capacity, the percentage of the grid filled by the moltenmetal was used. To evaluate shrinkage porosity, the rings from the treewere cut in half, embedded, polished and imaged under an opticalmicroscope. Image processing was then applied to measure the surfacefraction of pores. The above results are summarised in FIG. 7 .Comparative example 1 has low porosity, demonstrates good form fillingand can be considered highly castable. However, it does not meet thehardness requirement. The same is true for Comparative example 2, exceptit is less castable due to its poor form-filling ability. Comparativeexample 3 shows good form filling but has extensive shrinkage porosity(due to too large a solidification range) and may be considered too hardfor many jewellery applications. In contrast, Example 0 from thisinvention performs well on both castability metrics and is neither toohard nor too soft.

Machinability trials on showed that examples from this invention(Example 0) have superior machinability compared to the commonly usedComparative example 2. A CNC rig using tungsten carbide tooling was usedto machine a groove for gem setting in a simple ring. The comparison isshown in FIG. 8 —the machined groove in a band made of Comparativeexample 2 is full of burrs. Their presence is undesirable as removingthem is a time-consuming process. In contrast, Example 0 shows cleanedges. Unlike in Comparative example 2 small steps were observed in thegroove formed by subsequent tool passes. This indicates Example 0 issuitable for precision machining.

Results from additional casting trials on complex ring design are shownin FIG. 9 . Example 0 and Comparative example 2 were tested, both vacuuminvestment cast into flasks of essentially the same design. In bothcases, the melt was heated to approximately 200° C. above the meltingpoint before casting while the flask temperature was 732° C. While themost complex ring design (furthest back) was not fully filled by eitheralloy, Example 0 came much closer to complete fill. Example 0 also fullyfilled the ring at the front of the casting tree while the same designin Comparative example 2 (right-hand side of the casting tree) is showedonly a partial fill.

The alloy of example 0 is particularly promising and has excellentproperties. A particularly preferred alloy consists, in weight percent,of 0.0 to 2.0 indium, 0.0 to 5.0 nickel and 0.0 to 2.0 tin, with thebalance being platinum and incidental impurities, preferably 0.5 to 1.0indium, 3.0 to 4.0 nickel and 0.5 to 1.0 tin.

1-44. (canceled)
 45. A platinum alloy composition consisting, in weightpercent, of: 0.0 to 10.0 gold, 0.0 to 5.0 cobalt, 0.0 to 10.0 copper,0.0 to 7.0 iron, 0.0 to 4.0 gallium, 0.0 to 3.0 indium, 0.0 to 5.0iridium, 0.0 to 10.0 manganese, 0.0 to 7.0 nickel, 0.0 to 15.0palladium, 0.0 to 5.0 rhenium, 0.0 to 5.0 rhodium, 0.0 to 10.0ruthenium, 0.0 to 3.0 tin, 85.0 or more platinum and incidentalimpurities, wherein two or more of gallium, indium and tin are presentin an amount of 0.1 or more, wherein the following equation is satisfiedin which W_(Co), W_(Cu), W_(Fe), W_(Ga), W_(In), W_(Ni), W_(Pd), W_(Sn),W_(Rh), W_(Ir), W_(Au), W_(Ru), W_(Re) and W_(Mn) are the weight percentof cobalt, copper, iron, gallium, indium, nickel, palladium, tin,rhodium, iridium, gold, ruthenium, rhenium, and manganese in the alloyrespectively60+W _(Pd)*2.5+W _(Rh)*3.4+W _(Ir)*6.455+W _(Au)*11.93+W _(Ru)*13.241+W_(Cu)*14.328+W _(Re)*16.6+W _(Ni)*16.9+W _(Mn)*18.48+W _(Co)*18.69+W_(Fe)*21.879+W _(In)*29+W _(Sn)*28.207+W _(Ga)*42.379≥150 and whereinone of the following conditions is satisfied in which W_(Co), W_(Cu),W_(Fe), W_(Ga), W_(In), W_(Ni), W_(Pd), W_(Sn), W_(Mn), W_(Ru), W_(Ir),W_(Rh), W_(Au), W_(Pt) and W_(Re) are the weight percent of cobalt,copper, iron, gallium, indium, nickel, palladium, tin, manganese,ruthenium, iridium, rhodium, gold, platinum and rhenium in the alloyrespectively−0.1028*W _(Co)−0.1201*W _(Cu)−0.2113*W _(Fe)−0.3368*W _(Ga)−0.1125*W_(In)−0.1639*W _(Ni)−0.015*W _(Pd)−0.1959*W _(Sn)+17.276261−0.20*W_(Mn)+0.0678*W _(Ru)+0.035*W _(Ir)+0.045*W _(Rh)−0.059*W _(Au)+0.066*W_(Re)≤16.0 when W _(Pt)<95.0 and−0.1028*W _(Co)−0.1201*W _(Cu)−0.2113*W _(Fe)−0.3368*W _(Ga)−0.1125*W_(In)−0.1639*W _(Ni)−0.015*W _(Pd)−0.1959*W _(Sn)+17.276261−0.20*W_(Mn)+0.0678*W _(Ru)+0.035*W _(Ir)+0.045*W _(Rh)−0.059*W _(Au)+0.066*W_(Re)≤16.6 when W _(Pt)≥95.0 and wherein the following equations aresatisfied in which W_(Co), W_(Cu), W_(Fe), W_(Ga), W_(In), W_(Ni),W_(Pd), W_(Sn), and W_(Au) are the weight percent of cobalt, copper,iron, gallium, indium, nickel, palladium, tin, and gold in the alloy0.35W _(Au)+0.6W _(Sn)+0.6W _(In) +W _(Ga)≤3.75W _(Co) +W _(Pd) +W _(Fe) +N _(Ni) +W _(Cu≥)1.0W _(Sn) +W _(In) W _(Ga)≥0.25.
 46. The platinum alloy composition ofclaim 45, consisting, in weight percent, of 5.0 or less nickel,preferably 4.0 or less nickel.
 47. The platinum alloy composition ofclaim 45, wherein the following equation is satisfied in which WGa, WIn,and WSn are the weight percent of gallium, indium, and tin in the alloyWSn+WIn+WGa≥0.4.
 48. The platinum alloy composition of claim 45,consisting, in weight percent, of 2.5 or less indium, preferably 2.0 orless indium, preferably 1.0 or less indium.
 49. The platinum alloycomposition of claim 45, consisting, in weight percent, of 2.5 or lesstin, preferably 2.0 or less tin, more preferably 1.0 or less tin. 50.The platinum alloy composition of claim 45, wherein the alloycomposition has a solidification range of 200° C. or less, preferablywherein the alloy composition has a solidification range of 150° C. orless, more preferably wherein the alloy composition has a solidificationrange of 125° C. or less, more preferably wherein the alloy compositionhas a solidification range of 100° C. or less, even more preferablywherein the alloy composition has a solidification range of 75° C. orless, most preferably wherein the alloy composition has a solidificationrange of 50° C. or less.
 51. The platinum alloy composition of claim 45,wherein the following equation is satisfied in which WCo, WFe, WNi, andWPd are the weight percent of cobalt, iron, nickel, and palladium in thealloy respectively(W _(Co) +W _(Pd))/11+(W _(Fe) +W _(Ni))/2.2≥1.0
 52. The platinum alloycomposition of claim 45, consisting, in weight percent, of 2.0 or lessgallium, preferably 1.5 or less gallium.
 53. The platinum alloycomposition of claim 45, wherein the following equation is satisfied inwhich WIr and WRu are the weight percent of iridium and ruthenium in thealloy respectively2.5W _(Ir)+3.0W _(Ru)≤7.5
 54. The platinum alloy composition of claim45, wherein at least two, preferably at least three, elements selectedfrom the following list are present: gold, cobalt, copper, iron,gallium, indium, iridium, manganese, nickel, palladium, rhenium,rhodium, ruthenium, tin.
 55. The platinum alloy composition of claim 45,wherein the following equation is satisfied in which WCo, WCu, WFe, WNi,and WPd are the weight percent of cobalt, copper, iron, nickel andpalladium in the alloyW _(Co) +W _(Pd) +W _(Fe) +W _(Ni) +W _(Cu)≥2.0.
 56. The platinum alloycomposition of claim 45, wherein the following equation is satisfied inwhich WCo, WFe, and WNi, are the weight percent of cobalt, iron, andnickel in the alloy3.0≤W _(Co) +W _(Fe) +W _(Ni)≤4.5.
 57. The platinum alloy composition ofclaim 45, wherein the following equation is satisfied in which WGa, WIn,and WSn, are the weight percent of gallium, indium and tin in the alloy0.4≤W _(Ga) +W _(In) +W _(Sn)≤2.2.
 58. The platinum alloy composition ofclaim 45, wherein the two or more of gallium, indium and tin are indiumand gallium and the following equation is satisfied in which WGa andWIn, are the weight percent of gallium and indium in the alloy0.5W_(In)≤W_(Ga)≤1.5W_(In).
 59. The platinum alloy composition of claim45, wherein the two or more of gallium, indium and tin are tin andgallium and the following equation is satisfied in which WGa and WSn,are the weight percent of gallium and tin in the alloy0.5W_(Sn)≤W_(Ga)≤1.5W_(Sn)
 60. The platinum alloy composition claim 45,wherein the two or more of gallium, indium and tin are indium and tinand the following equation is satisfied in which WIn, and WSn, are theweight percent of indium and tin in the alloy0.5W_(In)≤W_(Sn)≤1.5W_(In)
 61. The platinum alloy composition claim 45,wherein the two or more of gallium, indium and tin are indium, tin andgallium and the following equations are satisfied in which WGa, WIn, andWSn, are the weight percent of gallium, indium and tin in the alloy0.3W_(In)≤W_(Ga)≤1.3W_(In)0.3W_(Sn)≤W_(Ga)≤1.3W_(Sn)0.3W_(In)≤W_(Sn)≤1.3W_(In)
 62. The platinum alloy composition of claim45, consisting of platinum, indium, nickel and tin.
 63. The platinumalloy composition of claim 45, consisting, in weight percent, of 0.5 ormore indium.
 64. A platinum alloy composition consisting, in weightpercent, of about 0.653 indium, about 3.405 nickel and about 0.654 tin,with the remainder being platinum and incidental impurities.